Add Security Scanner Configuration section and scanner CLI flags CI var

What does this MR do and why?

This MR includes the following:

• A section on Security Scanner Configuration - a provision for users to pass additional CLI options to the underlying security scanner in the SAST analyzer.
• Add --max-memory flag under Semgrep in the allowed flags
• CI Variable under Analyzer Setting: SAST_SCANNER_ALLOWED_CLI_OPTS - accepts a list of allowed flags forwarded to the security scanner as CLI options.

Relevant Issue numbers

• Introduce a generic SAST CI var to forward flag... (#368565 - closed)
• Accept --max-memory flag in SAST_SCANNER_ALLOWE... (#369388 - closed)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.