switch GCR -> Artifact-Registry

[ccwienk]

GCR has been deprecated [0] in favour of Artifact-Registry.

Thus, change push-targets for OCI-Images:

• europe-docker.pkg.dev/gardener-project/snapshots for snapshots
• europe-docker.pkg.dev/gardener-project/releases for releases
• europe-docker.pkg.dev/gardener-project/public for combined view of snapshots + releases

[0] https://cloud.google.com/artifact-registry/docs/transition/transition-from-gcr

Release note:

Change OCI Image Registry from GCR (`eu.gcr.io/gardener-project`) to Artifact-Registry (`europe-docker.pkg.dev/gardener-project/releases`). Users should update their references.

[gardener-robot-ci-2]

This PR proposes changes that would break the pipeline definition:

<invalid YAML>: mapping values are not allowed here
  in "<unicode string>", line 24, column 41:
     ...     - repository: ocm_repository: europe-docker.pkg.dev/gardener ... 
                                         ^

[gardener-robot-ci-3]

This PR proposes changes that would break the pipeline definition:

<invalid YAML>: mapping values are not allowed here
  in "<unicode string>", line 55, column 41:
     ...     - repository: ocm_repository: europe-docker.pkg.dev/gardener ... 
                                         ^

[gardener-robot-ci-2]

This PR proposes changes that would break the pipeline definition:

machine-controller-manager-provider-gcp-gcr-to-ar: Traceback (most recent call last):
  File "/usr/lib/python3.11/site-packages/concourse/replicator.py", line 141, in render
    definition_descriptor = self._render(definition_descriptor)
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/concourse/replicator.py", line 185, in _render
    'definition': factory.create_pipeline_definition(),
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/concourse/factory.py", line 83, in create_pipeline_definition
    variant = self._create_variant(
              ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/concourse/factory.py", line 138, in _create_variant
    variant._traits_dict = self._create_traits(raw_dict, variant_name)
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/concourse/factory.py", line 189, in _create_traits
    traits_dict = {
                  ^
  File "/usr/lib/python3.11/site-packages/concourse/factory.py", line 190, in <dictcomp>
    name: TraitsFactory.create(
          ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/concourse/model/traits/__init__.py", line 68, in create
    raise ModelValidationError('no such trait: ' + str(name))
model.base.ModelValidationError: no such trait: dockerimages

[gardener-robot-ci-2]

The pipeline-definition has been fixed.

[ccwienk]

@MartinWeindel | @kon-angelo : I am not sure how my suggested change might be related in detail to the test-error. please advise

[aaronfern]

@ccwienk I think the test error was a one off. I ran the tests again and they passed