[hotfix-v0.1] Switch GCR -> Artifact-Registry (gardener#22)

* cleanup: rm redundant/obsolete attributes

* switch GCR -> Artifact-Registry

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 read-access to
  snapshots + releases

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

---------

Co-authored-by: Christian Cwienk <[email protected]>

.ci/pipeline_definitions

@@ -1,21 +1,20 @@
 etcd-wrapper:
-  template: 'default'
   base_definition:
-    repo: ~
     traits:
       version:
         preprocess:
           'inject-commit-hash'
         inject_effective_version: true
+      component_descriptor:
+        ocm_repository: europe-docker.pkg.dev/gardener-project/snapshots
       publish:
         oci-builder: 'docker-buildx'
         platforms:
         - linux/amd64
         - linux/arm64
         dockerimages:
           etcd-wrapper:
-            registry: 'gcr-readwrite'
-            image: 'eu.gcr.io/gardener-project/gardener/etcd-wrapper'
+            image: europe-docker.pkg.dev/gardener-project/snapshots/gardener/etcd-wrapper
             dockerfile: 'Dockerfile'
             inputs:
               repos:
@@ -44,14 +43,22 @@ etcd-wrapper:
     head-update:
       traits:
         draft_release: ~
-        component_descriptor: ~
+        component_descriptor:
+          ocm_repository_mappings:
+            - repository: europe-docker.pkg.dev/gardener-project/releases
     pull-request:
       traits:
         pull-request: ~
     release:
       traits:
         version:
           preprocess: 'finalize'
+        component_descriptor:
+          ocm_repository: europe-docker.pkg.dev/gardener-project/releases
+        publish:
+          dockerimages:
+            etcd-wrapper:
+              image: europe-docker.pkg.dev/gardener-project/releases/gardener/etcd-wrapper
         release:
           nextversion: 'bump_minor'
         slack:
@@ -60,4 +67,3 @@ etcd-wrapper:
             internal_scp_workspace:
               channel_name: 'C0177NLL8V9' # gardener-etcd
               slack_cfg_name: 'scp_workspace'
-        component_descriptor: ~