XRAY-135041 slnx support added for dotnet

[Phavya-jfrog]

• The pull request is targeting the dev branch.
• The code has been validated to compile successfully by running go vet ./....
• The code has been formatted properly using go fmt ./....
• All static analysis checks passed.
• All tests have passed. If this feature is not already covered by the tests, new tests have been added.
• Updated the Contributing page / ReadMe page / CI Workflow files if needed.
• All changes are detailed at the description. if not already covered at JFrog Documentation, new documentation have been added.

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jf curation-audit silently skipped .NET projects with only a .slnx file, since technology detection never recognized it.

• Added .slnx to Nuget/Dotnet indicators and package descriptors.
• Fixed --solution-path not being passed into solution.Load() (was hardcoded to ""), which made solution.Load() auto-discover and merge projects from every solution file instead of honoring the explicit flag.
• Updated --solution-path flag description to mention .slnx.