Add support for dotnet in addition to mono

[redbaron]

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Is your feature request related to a problem? Please describe.

Github Actions upcoming ubuntu-22.04 image (currently in open beta) doesn't ship mono, which breaks nuget based caching.

Proposed solution
detect presence of dotnet and use it instead of mono.

Describe alternatives you've considered
Adding an alias from dotnet to mono seems to work, but it is a hack

[qc00]

Would expect more synergies between Microsoft projects than this silence...

Aliasing dotnet to mono (as some online posts suggest) does not work since vcpkg-tools seem to call mono natively.

[clee704]

I also want to see this happen as we're moving to CBL-Mariner from Ubuntu and Mariner doesn't ship mono.