ADGroup: Changing group membership management mechanism

[jeremyciak]

Pull Request (PR) description

This Pull Request is intended to change the way that the ADGroup resource manages group membership. The new implementation abandons usage of Add-ADGroupMember and Remove-ADGroupMember due to limitations with Foreign Security Principals. Instead we opt to utilize Set-ADGroup with the Add and Remove parameters, passing a hash object with the member key and a list of formatted SID values (e.g. - "<SID=SID_VALUE>").

• Fixes #619

  Task list

• [x] Added an entry to the change log under the Unreleased section of the file CHANGELOG.md. Entry should say what was changed and how that affects users (if applicable), and reference the issue being resolved (if applicable).
• [x] Resource documentation added/updated in README.md.
• [ ] Resource parameter descriptions added/updated in README.md, schema.mof and comment-based help.
• [x] Comment-based help added/updated.
• [x] Localization strings added/updated in all localization files as appropriate.
• [x] Examples appropriately added/updated.
• [x] Unit tests added/updated. See DSC Community Testing Guidelines.
• [ ] Integration tests added/updated (where possible). See DSC Community Testing Guidelines.
• [x] New/changed code adheres to DSC Community Style Guidelines.

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This change is 

[codecov[bot]]

Codecov Report

Merging #621 into master will increase coverage by 0%. The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #621    +/-   ##
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  Coverage      98%    98%            
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  Files          24     24            
  Lines        3110   3208    +98     
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+ Hits         3049   3149   +100     
+ Misses         61     59     -2