Opt-in CPM for buildcheck template

[JanKrivanek]

Context

We are having Microsoft.Build package version managed centrally - but we do not opt-in to the feature - as a result restore will not respect our setting in Directory.Build.props.

Testing

Manual runs

Before:

  C:\repro\Contoso.BuildChecks.csproj : warning NU1604: Project dependency Microsoft.Build does not contain an inclusive lower bound. Include a lower bound in the dependency version to ensure consistent restore results.

  (...)

  C:\repro\Contoso.BuildChecks\Check1.cs(2,23): error CS0234: The type or namespace name 'Experimental' does not exist in the namespace 'Microsoft.Build' (are you missing an assembly reference?)

  (...)
  Build failed with 8 error(s) and 2 warning(s) in 1.6s

After:

 (...)
 Build succeeded with 12 warning(s) in 3.0s

Note: The warnings in the sample above are caused by unrelated issues (will be tracked separately)