tool-cache.getManifestFromRepo() has hard coded URL and does not support GHES repo

[ganadist]

Describe the enhancement
I tried to improve setup-python that user can provide versions-manifest.json ( actions/setup-python#717 )
And after apply above change, and I tried to use above modification at Github Enterprise Server.

But I found that current implementation of tool-cache has hardcoded URL (https://api.github.com) and it does not support GHES endpoint URL (https://GHES/api/v3), yet.
https://github.com/actions/toolkit/blob/45c49b0/packages/tool-cache/src/tool-cache.ts#L596

So, manifest is always fetched from github.com.

IMHO, for GHES users, if getManifestFromRepo() is called at GHES instances, this should search manifest from GHES first, and get manifest from github.com as fallback. (similar behavior when actions were fetched on GHES self-runners).

Code Snippet
If applicable, add a code snippet to show the api enhancement.

Additional information
Add any other context about the feature here.