Simplify and streamline documentation content across multiple pages

[mintlify]

Original Instruction: rewrite our quickstart page in more simple, concise writing

This PR simplifies and improves the readability of our documentation content, focusing on making the writing more concise and accessible. While the original instruction targeted the quickstart page, the changes extend to multiple documentation sections for consistency in writing style.

Changes include:

• Simplified and streamlined the quickstart page content
• Updated related documentation pages to maintain consistent writing style
• Improved clarity across various integration guides
• Enhanced readability of authentication and personalization documentation
• Refined SDK and analytics integration documentation

Modified files:

• Core documentation: quickstart.mdx, development.mdx, web-editor.mdx, reusable-snippets.mdx
• Widget and API documentation: advanced/widget/chat.mdx, api-playground related files
• Multiple integration guides: analytics, privacy, SDKs, and support
• Authentication and personalization settings

These changes aim to make our documentation more user-friendly and easier to understand while maintaining technical accuracy.