Add option to Merge or Overwrite Bits in Add-VSTeamAccessControlEntry

[mrwalters1988]

PR Summary

This enables the option mentioned in the inline comments of Add-VSTeamAccessControlEntry to choose whether to merge the Bits or to Overwrite the bits.

PR Checklist

• [x] Write Help
• [x] Write Unit Test
• [x] Update CHANGELOG.md

[mrwalters1988]

I didn't see any changes that needed to be made in the tests, and changelog looks like it's only updated when several PRs are approved and merged in, so I did not update that either. Can do so if needed.

[mrwalters1988]

Any update on this?

[mrwalters1988]

Thanks @SebastianSchuetze I had set aside time next week to add the unit test, but I appreciate you adding it for me. Happy to have contributed.