Improve handling of pekko versions in scala-akka-http-server generator

[bjolletz]

This change is a fix for Issue 20225 - Improve handling of pekko versions
#20275

This change adds a new parameter for the scala-akka-http-server generator. The parameter is called pekkoHttpVersion and lets a user control the version of the pekko-http package in the same way you do for akka-http versions.

The change also increases the version of pekko-stream to 1.0.3.

To validate the work in this PR, run the scala-akka-http-generator:

• Not using the usePekkoHttp flag should have the same bahavior as before
• usePekkoHttp=true should add pekko packages instead of akka packages just as before, but the pekko-stream package should now have version 1.0.3. The version of pekko-http should still be 1.0.0 as long as the pekkoHttpVersion parameter is not provided.
• usePekkoHttp=true and pekkoHttpVersion=someVersion should result in pekko packages being used instead of akka and the version of pekko-http should be whatever was provided in the pekkoHttpVersion paramater.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
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  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in Git BASH)
  Commit all changed files.
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@clasnake , @shijinkui , @ramzimaalej , @chameleon82 , @Bouillie , @Fish86

[ramzimaalej]

LGTM

[wing328]

https://github.com/OpenAPITools/openapi-generator/actions/runs/12252917548/job/34180935976?pr=20277

please update the samples when you've time