Add SAST Code Review Process and template

Why is this change being made?

Adds Static Analysis Group Code Review Process page documenting the code review process for groupstatic analysis.

Current items uncovered by this are:

1. a section on the current exceptions to this process regarding initial maintainers
   • reserving merge rights for trainee maintainers
   • "graduation" from trainee maintainership
   • issue template needs a notice around expected cadence to avoid stale issues and auto-closure
   • notice that merge rights for trainees will be maintained on all projects until initial maintainer(s) is established
2. EM is responsible for helping guide trainee issues until maintainers are established
3. Not all projects are created equal and may warrant exceptions to bucketing (example: spotbugs is more complex than pmd-apex)

None of which are blockers and we can follow-up with any as we see fit

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files. (this requirement has been removed pending identification of a new DRI for the handbook)