add membership functions

[Seekatar]

PR Summary

Added functions to add/delete/get Memberships. I didn't add a type or format in this PR since memberships are just two ids. I'd like to do another PR to add a Permissions container to the PSDrive with Group and User child items.

PR Checklist

• Write Help
• Write Unit Test
• Update VSTeam.psd1
• Update CHANGELOG.md

[Seekatar]

I see the build failed in the UT, but I can't reproduce locally on PS 5,6, or 7. All succeed for me.

[DarqueWarrior]

reviewing now. Sometimes it fails due to the lack of permissions of PR builds.

[DarqueWarrior]

Can you clear this warning?
##[warning]dist\vsteam.functions.ps1(5507,10): Warning : Function 'Remove-VSTeamMembership' has verb that could change system state. Therefore, the function has to support 'ShouldProcess'.

[Seekatar]

Warning fixed.
Btw, I work with Jeffery at Clear-Measure and I've been using VSTeam for automating AzDo for a while. I added some extensions, and am finally getting around to making some PRs. Great lib!

[Seekatar]

I think the UT error is the cached call to project. I added code I saw from other tests to avoid calling it.

[DarqueWarrior]

Sorry for delay. I will try to get to this this week.