Use environment variables in minver-cli

[adamralph]

Thanks to @augustoproiete for raising #423 for MinVerBuildMetadata, which led to this more general enhancement.

The MinVer package accepts options as environment variables. This is standard .NET SDK behaviour: all environment variables are propagated as MSBuild properties.

With this enhancement, the minver-cli package does the same thing.

There is one exception: MinVerSkip. This option effectively switches off the MinVer package, which means none of the output properties will be set, which means the SDK will use whatever version is set via a Version property, whether that is explicitly done for a project, or implicitly done by the SDK as a default value. There is no good equivalent for minver-cli. If the command line were "switched off", then the equivalent behaviour would be to return no value. If a user wants to "switch off" the minver-cli package, then they can observe MinVerSkip themselves and provide an alternate version string in that scenario.

[adamralph]

Released in 2.4.0-beta.1.

@augustoproiete please give it a try.

[augustoproiete]

Cheers @adamralph! I will take it for a spin!

Update: Test results