Install-SqlDscServer: Fix bug for PrepareImage

[johlju]

Pull Request (PR) description

• Install-SqlDscServer
  • Now the parameter InstanceName can no longer be specified (as per
    the SQL Server documentation) for the setup action PrepareImage
    (issue Install-SqlDscServer with -PrepareImage errors when InstanceName is specified #1960).

This Pull Request (PR) fixes the following issues

• Fixes Install-SqlDscServer with -PrepareImage errors when InstanceName is specified #1960

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 

[codecov]

Codecov Report

Merging #1961 (43f1310) into main (22c4f2d) will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff          @@
##           main   #1961   +/-   ##
====================================
  Coverage    91%     91%           
====================================
  Files        92      92           
  Lines      7810    7810           
====================================
  Hits       7185    7185           
  Misses      625     625           

Flag	Coverage Δ
unit	91% <ø> (ø)

Files Changed	Coverage Δ
source/Private/Invoke-SetupAction.ps1	92% <ø> (ø)
source/Public/Install-SqlDscServer.ps1	100% <ø> (ø)

[johlju]

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @johlju)