xUser: add NewName property

[gaelicWizard]

Pull Request (PR) description

Adds optional parameter NewName to User resource to allow setting SamAccountName property separately. This requires that UserName 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.

---

This change is 

[codecov]

Codecov Report

Merging #719 (50d4159) into main (dcadffd) will decrease coverage by 0%.
The diff coverage is 50%.

@@         Coverage Diff         @@
##           main   #719   +/-   ##
===================================
- Coverage    72%    72%   -1%     
===================================
  Files        30     30           
  Lines      4427   4457   +30     
===================================
+ Hits       3213   3228   +15     
- Misses     1214   1229   +15     

Impacted Files	Coverage Δ
...Resources/DSC_xUserResource/DSC_xUserResource.psm1	53% <50%> (-1%)	⬇️