docs: add NestJS security cheatsheet

[Riya-chandra]

Description

This PR introduces a new mini-cheatsheet specifically for NestJS security best practices. While the current Node.js sheet covers Express, this addition provides framework-native patterns for NestJS's unique architecture.

Key Sections:

Request Lifecycle: Strategic placement of security controls across Middleware, Guards, and Pipes.

Input Validation: Strict ValidationPipe setup to mitigate Mass Assignment risks.

Secure Defaults: Hardened Helmet and CORS configurations.

This PR fixes issue #1986.

Verification Results

• Technical Accuracy: Snippets verified against NestJS v10+ standards.

• Local Build: Verified that the new sheet renders correctly in the navigation under "Languages and Frameworks" using mkdocs serve.

• Style: Content is kept concise as requested by the maintainers.

Thank you!

[jmanico]

This is a well organized piece of work and I like it.

[Riya-chandra]

@jmanico Thankyou sir

[bad-antics]

Great contribution! This will be helpful for the community. 🔥

[RushabhRatnaparkhi]

Thanks for the great work!
I’ve read through the cheatsheet — it’s clear and practical.
Happy to help with any follow-ups, fixes, or small improvements if needed after merge.

[jmanico]

Please carefully add your new cheatsheet here in this PR.

https://github.com/OWASP/CheatSheetSeries/blob/master/Index.md

[Riya-chandra]

@jmanico i have added the cheatsheet in the index.md......please have a look
Thankyou

[jmanico]

Please give us time for the other reviewers to review this.

[jmanico]

lint errors in markdown:

cheatsheets/NestJs_Security_Cheat_Sheet.md:31 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "bash"] cheatsheets/NestJs_Security_Cheat_Sheet.md:36 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:55 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"] cheatsheets/NestJs_Security_Cheat_Sheet.md:78 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "bash"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:95 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "bash"] cheatsheets/NestJs_Security_Cheat_Sheet.md:100 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:119 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"] cheatsheets/NestJs_Security_Cheat_Sheet.md:138 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:152 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"] cheatsheets/NestJs_Security_Cheat_Sheet.md:172 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:189 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "bash"] cheatsheets/NestJs_Security_Cheat_Sheet.md:194 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:223 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"] cheatsheets/NestJs_Security_Cheat_Sheet.md:241 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "env"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:246 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"] cheatsheets/NestJs_Security_Cheat_Sheet.md:259 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "bash"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:264 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"] cheatsheets/NestJs_Security_Cheat_Sheet.md:287 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:302 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "Safe: Use Repository Pattern"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:303 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"] cheatsheets/NestJs_Security_Cheat_Sheet.md:310 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "Safe: Query Builder with Param..."] cheatsheets/NestJs_Security_Cheat_Sheet.md:311 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:320 MD036/no-emphasis-as-heading Emphasis used instead of a heading [Context: "Vulnerable: String Concatenati..."]
cheatsheets/NestJs_Security_Cheat_Sheet.md:321 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"] cheatsheets/NestJs_Security_Cheat_Sheet.md:331 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:340 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"] cheatsheets/NestJs_Security_Cheat_Sheet.md:366 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:379 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "bash"] cheatsheets/NestJs_Security_Cheat_Sheet.md:384 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:404 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"] cheatsheets/NestJs_Security_Cheat_Sheet.md:413 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:442 MD031/blanks-around-fences Fenced code blocks should be surrounded by blank lines [Context: "```typescript"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:450 MD022/blanks-around-headings Headings should be surrounded by blank lines [Expected: 1; Actual: 0; Below] [Context: "### Before Production:"]
cheatsheets/NestJs_Security_Cheat_Sheet.md:450:22 MD026/no-trailing-punctuation Trailing punctuation in heading [Punctuation: ':']
cheatsheets/NestJs_Security_Cheat_Sheet.md:451 MD032/blanks-around-lists Lists should be surrounded by blank lines [Context: "- [ ] ValidationPipe configure..."]
Error: Process completed with exit code 1.