Security cmdlet Improvements and added Add-VSTeamBuildPermission

[SebastianSchuetze]

PR Summary

• added the cmdlet Add-VSTeamBuildPermission following the other cmdlet like Add-VSTeamProjectPermission
• changed internal functions to not have deny or allow permissions to be mandatory, because this caused not to be able to only add allow or deny permissions.
• allowed to handle user accounts from typ 'srv' which are service accounts of Azure DevOps. Now these can be permitted as well to all functions using ACLs

PR Checklist

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

[SebastianSchuetze]

made a mistake with commits and branching. Closing this pull request and reopen a new one with a clean branch