[RFE][k8s] Include `upstream-source` field information at Release

[phvalguima]

Currently, charms are publishing its OCI image revision (e.g.: https://github.com/canonical/mysql-k8s-operator/releases/tag/rev132), however to discover the source of that given revision, we need to check the specific commit's metadata.yaml.

To make it easier for support, can we also attach that information to the releases?

[github-actions]

https://warthogs.atlassian.net/browse/DPE-3923

[carlcsaposs-canonical]

Since it's in a standardized format, this seems like a good idea

As with #160, would like to see something for this maybe land in charmcraft or get standardized across VM and K8s charms instead of K8s only