Add changed port tests workflows

[m-kuhn]

Add workflows to test changed ports:

triplets:

• x64-linux
• x64-osx
• x64-windows
• (android / ios / upstream unsupported linux/osx dynamic triplets? possibly later)

which vcpkg baseline to use? latest tag with dependabot/renovate updates? current master?
how to detect changed ports?

Compare

• https://github.com/luncliff/vcpkg-registry/tree/main/.github/workflows (no changed port detection, rebuilds the registry world with a dummy manifest in the test folder)
• https://github.com/microsoft/vcpkg/blob/master/scripts/azure-pipelines/test-modified-ports.ps1#L150-L168 vcpkg ci based approach, check how to handle parent-hashes.json