Allow the user to set the package version when running the azdo pipeline

[AdamYoblick]

Fixes #8149

This allows the user to explicitly set the package version when running the azdo pipeline. Normally, using $(Build.BuildNumber) works just fine. But VS is strict about version relationships between their release branches, and we need to be able to patch the 17.10 branch with the new version still being lower than 17.11+ and also lower than main. Since the build numbers are always increasing, there isn't a way to do this currently.

So this change enables this functionality. The value will be set to the current build number if the user doesn't specify a version (the value can't be an empty string for runtime parameters unfortunately, so I set the default to currentBuildNumber. Otherwise, the value will be set to whatever the user specifies.

Testing

IN PROGRESS

1. I ran our build pipeline, pointing at the set_package_version branch. That run is at https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=10920395&view=results. I left the PTVS package version as the default value of currentBuildNumber. Then I downloaded the bootstrapper from our build artifacts and ran it, installing the Python workload. I verified that the version in Help -> About matched the build number:

2. I ran our build pipeline, pointing at the set_package_version branch. That run is at https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=10920896&view=results. I set the PTVS package version to 9999.99. Then I downloaded the bootstrapper from our build artifacts and ran it, installing the python workload. I verified that the version in Help -> About matched the version I set:

[AdamYoblick]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud