ci: migrate from GitLab CI to Gitea Actions

- Add Gitea Actions workflow (.gitea/workflows/ci.yaml)
- Update K8s deployment image registry to oci.unbound.se

k8s/deploy.yaml

@@ -13,7 +13,7 @@ spec:
         spec:
           containers:
             - name: dancefetcher
-              image: registry.gitlab.com/unboundsoftware/dancefinder/dancefetcher:${COMMIT}
+              image: oci.unbound.se/dancefinder/dancefetcher:${COMMIT}
               imagePullPolicy: Always
               resources:
                 limits: