SqlServerDsc: Re-enable Pester's new code coverage method

[johlju]

Pull Request (PR) description

• SqlServerDsc
  • Add empty constructor to classes to be able to use Pester's new code coverage method. See more information can be found in pester/Pester#2306.

This Pull Request (PR) fixes the following issues

None.

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).
• [ ] 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.
• [x] Code changes adheres to DSC Community Style Guidelines.

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This change is 

[codecov[bot]]

Codecov Report

Merging #1857 (f93c50e) into main (38a0da4) will increase coverage by 0%. The diff coverage is n/a.

@@         Coverage Diff          @@
##           main   #1857   +/-   ##
====================================
  Coverage    91%     92%           
====================================
  Files        85      85           
  Lines      7608    7608           
====================================
+ Hits       6952    7006   +54     
+ Misses      656     602   -54     

Flag	Coverage Δ
unit	92% <ø> (+<1%)	:arrow_up:

Impacted Files	Coverage Δ
source/Classes/002.DatabasePermission.ps1	100% <ø> (ø)
source/Classes/002.ServerPermission.ps1	100% <ø> (ø)
source/Classes/004.StartupParameters.ps1	100% <ø> (ø)
source/Public/Set-SqlDscTraceFlag.ps1	90% <0%> (-10%)	:arrow_down:
source/Classes/011.SqlResourceBase.ps1	83% <0%> (-9%)	:arrow_down:
source/Public/Get-SqlDscManagedComputerService.ps1	95% <0%> (-5%)	:arrow_down:
source/Public/Add-SqlDscTraceFlag.ps1	95% <0%> (-5%)	:arrow_down:
source/Public/Remove-SqlDscTraceFlag.ps1	96% <0%> (-4%)	:arrow_down:
source/Public/Set-SqlDscStartupParameter.ps1	96% <0%> (-4%)	:arrow_down:
source/Classes/020.SqlAudit.ps1	99% <0%> (-1%)	:arrow_down:
... and 24 more