Add GitHub Action to run PSScriptAnalyzer on PR and commit

[fflaten]

PR Summary

Adds a workflow that scans source code for good practices on commit to main-branch and in pull requests.

Trying GitHub Action first to enable feedback in PRs. If it's too noisy, PR-trigger can be disabled or we could move this to AzDO CI (see example)

Results will show up both in:

• Security -> Code scanning alerts
  

• And as code review/comment for any affected code in pull requests
  

Fix #1635

PR Checklist

• PR has meaningful title
• Summary describes changes
• PR is ready to be merged
  • If not, use the arrow next to Create Pull Request to mark it as a draft. PR can be marked Ready for review when it's ready.
• Tests are added/update (if required)
• Documentation is updated/added (if required)