Add package validation to NuGet publishing (OSOE-176)

[Piedone]

The .NET SDK has package validation, which are useful checks when you publish your NuGet package. Let's utilize them, and configure them how we see them suitable.

• Baseline version validator:
  • We already have the previous version lookup code in the publish-nuget action to get the baseline version. This needs to compare against the latest release (i.e. not pre-release/alpha) version. Note that there might not be a previous release yet, in which case this validation shouldn't run.
  • What to do during alpha releases, releases for issues? Breaking changes should still be tackled, but we need to be able to accept them. The CompatibilitySuppressions.xml file is good for this, but this also needs to be automatically removed upon a major release (i.e. when we may introduce breaking changes).
• Compatible runtime validator looks good as it is.
• Compatible framework validator looks good as it is.
• Do everything from the CLI if possible, without the need to modify csprojs.

[Piedone]

Didn't use Baseline version validator in the workflow in the end. It would require constant maintenance of the suppression file. Instead, documented to run it prior to selecting the next version number.