Decommission usage Artifact.Checksum field

[hiddeco]

In #1001 the Artifact.Checksum field has been deprecated in favor of the newly introduced Artifact.Digest. This PR itself did not decommission the usage of the field throughout the controller itself, as the controller may be backed by a Persistent Volume which would not cause it to produce a digest until a new artifact has been stored, allowing a transition period to exist.

Full deprecation of this field could either be done in a single stage in which we remove the Checksum field from the Artifact and start working solely with the Digest. Or we can opt to first check if a Digest is present before falling back to the Checksum, while not removing the field yet from the API.

Internals

• Use Digest when available, optionally falling back to Checksum

API facing

• Remove Checksum field from Artifact
• Remove calculation of SHA-256 sum on storage of Artifact

xref: #1001 (comment)