SqlAGReplica: Converted unit tests to Pester 5

[johlju]

Pull Request (PR) description

• SqlAgReplica
  • Converted unit test to Pester 5.
  • No longer tries to enforce EndpointHostName when it is not part of the
    configuration (issue SqlAGReplica: Enforce EnpointHostName even though it is not part of the configuration #1821).
  • Now Get-TargetResource always returns values for the properties Name
    and AvailabilityGroupName (issue SqlAGReplica: Get-TargetResource does not return key properties when absent #1822).
  • Now Test-TargetResource no longer test properties that cannot
    be enforced (issue SqlAGReplica: Get-TargetResource does not return key properties when absent #1822).

This Pull Request (PR) fixes the following issues

• Fixes SqlAGReplica: Refactor unit tests to support Pester 5 #1753
• Fixes SqlAGReplica: Enforce EnpointHostName even though it is not part of the configuration #1821
• Fixes SqlAGReplica: Get-TargetResource does not return key properties when absent #1822

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 updated in the resource's README.md.
• Resource parameter descriptions updated in schema.mof.
• Comment-based help updated, including parameter descriptions.
• Localization strings updated.
• Examples updated.
• Unit tests updated. See DSC Community Testing Guidelines.
• Integration tests updated (where possible). See DSC Community Testing Guidelines.
• Code changes adheres to DSC Community Style Guidelines.

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This change is 

[johlju]

I converted the tests for Get so far. The rest are coming in other commits.

[codecov]

Codecov Report

Merging #1820 (c3b7b2e) into main (d5692e2) will increase coverage by 2%.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           main   #1820    +/-   ##
=====================================
+ Coverage    88%     90%    +2%     
=====================================
  Files        82      82            
  Lines      7437    7437            
=====================================
+ Hits       6588    6737   +149     
+ Misses      849     700   -149     

Flag	Coverage Δ		*Carryforward flag
unit	90% <100%> (+2%)	⬆️	Carriedforward from bee3ad5

*This pull request uses carry forward flags. Click here to find out more.

Impacted Files	Coverage Δ
...SCResources/DSC_SqlAGReplica/DSC_SqlAGReplica.psm1	75% <100%> (+75%)	⬆️

[johlju]

Converted Set-TargetResource. I will convert Test-TargetResource tomorrow.

[johlju]

Reviewed 3 of 3 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @johlju)