[vcpkg] Ability to use git tags as baseline in manifest files

[gvnnz]

Currently, the builtin-baseline key accepts only a commit sha. It would be nice to specify tag names as well, for example:

...
"builtin-baseline": "2022.03.10",
...

[AugP]

This is a good suggestion, I've added it to our backlog. We're booked through the end of September currently, but we'll consider it for the semester beginning in October during our planning.

[ghost]

Bumping this. See #27583