Add SAST default analyzer strings and missing SAST analyzer

What does this MR do?

This MR is to update SAST analyzer documentation to include missing analyzer PMD Apex and add the list of strings of analyzers that can be used with the SAST_DEFAULT_ANALYZERS variable. I have made changes similar to what we have in dependancy scanning doc where the strings of dependency scanners are there straight away.

Does this MR meet the acceptance criteria?

Conformity

• Documentation created/updated
• Follow the Documentation Guidelines and Style Guide.
• Link docs to and from the higher-level index page, plus other related docs where helpful.
• Apply the ~Documentation label.

Review checklist

All reviewers can help ensure accuracy, clarity, completeness, and adherence to the Documentation Guidelines and Style Guide.

1. Primary Reviewer

• Review by a code reviewer or other selected colleague to confirm accuracy, clarity, and completeness. This can be skipped for minor fixes without substantive content changes.

2. Technical Writer

• Optional: Technical writer review. If not requested for this MR, must be scheduled post-merge. To request for this MR, assign the writer listed for the applicable DevOps stage.

3. Maintainer

1. Review by assigned maintainer, who can always request/require the above reviews. Maintainer's review can occur before or after a technical writer review.
2. Ensure a release milestone is set and that you merge the equivalent EE MR before the CE MR if both exist.
3. If there has not been a technical writer review, create an issue for one using the Doc Review template.

~Documentation