Added copilot security config

[vietle-cgi]

This PR adds shared GitHub Copilot settings and a .copilotignore file.

What this does:

• Prevents Copilot from automatically using certain files (e.g. config files, .env, .json, .yaml) as background context when generating suggestions
• Disables inline Copilot suggestions for all files by default, and enables them only for specified languages
• Helps reduce accidental exposure of sensitive configuration in Copilot suggestions
• Makes Copilot behavior consistent across the team

What this does NOT do (important):

• It does not stop Copilot from reading a file if a developer explicitly opens it and asks Copilot to explain or analyze it (for example using Ctrl + I)
• It cannot prevent intentional use of Copilot on these files

In short, this change limits automatic Copilot usage but does not block explicit user actions.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud