Allow users to update a generic Artifact

[lampajr]

Is your feature request related to a problem? Please describe.
With this PR https://github.com/opendatahub-io/model-registry/pull/289 we extended the Artifact types with a new DocArtifact.

DocArtifact can be added using versions/<id>/artifacts endpoint but there is no way to update them once created, I think that it is worth to consider adding some endpoints for generic get and patch of a generic artifact.

Describe the solution you'd like
Add some endpoints for generic get and patch (and post ?) of a generic artifact.

Describe alternatives you've considered
n/a

Additional context
n/a