Remove external CRD artifact from repository

[frewilhelm]

Description

Currently, our controller repository contains references to the artifact crd in the Makefile, config/crd/bases/openfluxcd.ocm.software_artifacts.yaml, and config/default/kustomization.yaml.

Makefile: Contains targets to download external crds download-crd-deps. However, until now it only refers to the artifact crd.
config/crd/bases/openfluxcd.ocm.software_artifacts.yaml: Contains an exact copy of https://github.com/openfluxcd/artifact/blob/main/config/crd/bases/openfluxcd.ocm.software_artifacts.yaml
config/default/kustomization.yaml: Contains a link to https://raw.githubusercontent.com/openfluxcd/artifact/refs/tags/v0.1.1/config/crd/bases/openfluxcd.ocm.software_artifacts.yaml which is - again - a reference to the already copied and referenced artifact crd.

All these references seem a bit hard to maintain (which was already reported, when we changed the gvk of artifact).

Additionally, I would argue that such external CRD should not be copied in our controller repository. This harms the principle of a single source of truth.

I would even go so far as to argue that we should not make any reference to this artifact CRD in this repository as the hardcoded definition on a pinned version limits the user and developer in their scope. I would propose that users have to deploy/install their artifact CRD themselves (as it is also required for the helm- and kustomize-controller).

Done Criteria

• ...
• Code has been reviewed by other team members
• Internal technical Documentation created/updated
• New / changed code is documented
• Analysis of existing tests (Unit and Integration)
• Unit Tests created for new code or existing Unit Tests updated
• Integration Test Suite updated (includes deletion of existing unnecessary Integration Test and/or creation of new ones if required)
• Enduser Documentation updated (if applicable)
• Successful demonstration in Review