chore(ci): add own registry to buildx config

.woodpecker/.build.yaml

@@ -1,12 +1,25 @@
+variables:
+  - publish_mirror: &publish_mirror
+      from_secret: DOCKER_MIRROR_URL
+  - publish_logins: &publish_logins
+      - registry:
+          from_secret: DOCKER_MIRROR_URL
+        username:
+          from_secret: DOCKER_MIRROR_USER
+        password:
+          from_secret: DOCKER_MIRROR_PASS
+      - registry: git.ar21.de
+        username:
+          from_secret: REGISTRY_USER
+        password:
+          from_secret: REGISTRY_PASS
+
 steps:
 - name: docker
   image: woodpeckerci/plugin-docker-buildx
   settings:
-    registry: git.ar21.de
-    username:
-      from_secret: REGISTRY_USER
-    password:
-      from_secret: REGISTRY_PASS
+    mirror: *publish_mirror
+    logins: *publish_logins
     repo: git.ar21.de/yolokube/go-traefik-certmanager
     platforms:
       - linux/amd64
@@ -20,11 +33,8 @@ steps:
 - name: docker-staging
   image: woodpeckerci/plugin-docker-buildx
   settings:
-    registry: git.ar21.de
-    username:
-      from_secret: REGISTRY_USER
-    password:
-      from_secret: REGISTRY_PASS
+    mirror: *publish_mirror
+    logins: *publish_logins
     repo: git.ar21.de/yolokube/go-traefik-certmanager
     platforms:
       - linux/amd64