ci: add woodpecker ci for container image builds

.woodpecker/build-image.yml

@@ -0,0 +1,15 @@
+when:
+  - event: [push]
+steps:
+  - name: build
+    image: woodpeckerci/plugin-kaniko
+    settings:
+      registry: gitea.cazzzer.com
+      repo: ${CI_REPO,,}
+      # replace '/' in branch name
+      tags: ${CI_COMMIT_BRANCH/\//-}
+      cache: true
+      username:
+        from_secret: registry-username
+      password:
+        from_secret: registry-password