feat(datasource/github-releases)!: digest computation use git tag, not file digest (#20178)

The github-releases datasource has been copied into a new datasource called github-release-attachments.
The github-releases general datasource is updated to use the underlying Git tag of a GitHub release entry for digest computation.

Fixes #20160, Fixes #19552

BREAKING CHANGE: Regex Manager configurations relying on the github-release data-source with digests will have different digest semantics. The digest
will now always correspond to the underlying Git SHA of the release/version. The old behavior can be preserved by switching to the
github-release-attachments datasource.