feat(new): Added Azure.PostgreSQL.MaintenanceWindow

[BenjaminEngeset]

PR Summary

Fixes #2927

Added Azure.PostgreSQL.MaintenanceWindow rule.

PR Checklist

• [x] PR has a meaningful title
• [x] Summarized changes
• [x] Change is not breaking
• [x] This PR is ready to merge and is not Work in Progress
• Rule changes
  • [x] Unit tests created/ updated
  • [x] Rule documentation created/ updated
  • [x] Link to a filed issue
  • [x] Change log has been updated with change under unreleased section
• Other code changes
  • [ ] Unit tests created/ updated
  • [ ] Link to a filed issue
  • [ ] Change log has been updated with change under unreleased section

[BenjaminEngeset]

Ready for review @BernieWhite, similar as the MySQL, just changed the resource type.