Add SAST, Secret Detection and Code quality docs
What's Changed
- Added an introductory paragraph in Secure your application section
- Added pages for SAST and Secret Detection under this section
- Added a page for Code Quality Analysis under Build your Application section
Why
- Updates required for adding documentation on GitLab Security and Code Quality features
Sections Affected
- Secure your application
- Build your Application
How was it tested
- Checked MD preview on online GitLab IDE
Anything Else
-