[vcpkg-tool] Allow baseline to use a tag as well as commit sha

[GordonSmith]

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

Its frustrating when viewing vcpkg-configuration.json files that have a baseline which refers to a specific tag as we must use a commit SHA, which doesn't convey any "when" or "version" information:

{
  "default-registry": {
    "kind": "git",
    "baseline": "9edb1b8e590cc086563301d735cae4b6e732d2d2",
    "repository": "https://github.com/microsoft/vcpkg"
  },
  "overlay-ports": [
    "./vcpkg-overlays"
  ],
  "overlay-triplets": [],
  "registries": []
}

Proposed solution

What would be better IMO would be to allow tags:

{
  "default-registry": {
    "kind": "git",
    "baseline": "2023.08.09",
    "repository": "https://github.com/microsoft/vcpkg"
  },
  "overlay-ports": [
    "./vcpkg-overlays"
  ],
  "overlay-triplets": [],
  "registries": []
}

Describe alternatives you've considered

NA

Additional context

No response