xGroup: add NewName property

[gaelicWizard]

Pull Request (PR) description

Adds optional parameter NewName to xGroup resources to allow setting SamAccountName property separately. This requires that GroupName be specified using something other than the SamAccountName, e.g. SID.

This Pull Request (PR) fixes the following issues

• See alsö ADUser, ADGroup: Specify samAccountName separately ActiveDirectoryDsc#655

Task list

• 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).
• Resource documentation added/updated in README.md.
• Resource parameter descriptions added/updated in README.md, schema.mof
  and comment-based help.
• Comment-based help added/updated.
• Localization strings added/updated in all localization files as appropriate.
• Examples appropriately added/updated.
• Unit tests added/updated. See DSC Community Testing Guidelines.
• Integration tests added/updated (where possible). See DSC Community Testing Guidelines.
• New/changed code adheres to DSC Community Style Guidelines.

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This change is