feat(ci): Maintain up to 1 open MR in the k8s repo per DRE branch (#298)

This will provide us with flexibility to deploy from separate branches in the DRE repo (if needed), and still keep the number of MRs in k8s repo small and bounded.

.github/workflows/update-k8s-deployments/action.yaml

@@ -27,8 +27,8 @@ runs:
         cd k8s
         git config user.email "idx@dfinity.org"
         git config user.name "IDX Automation"
-        DRE_REPO_BRANCH="${{ github.head_ref || github.event.pull_request.head.ref }}"
-        K8S_REPO_BRANCH="update-dre-images"
+        DRE_REPO_BRANCH="${{ github.head_ref || github.ref_name }}"
+        K8S_REPO_BRANCH="update-dre-images-$DRE_REPO_BRANCH"
         git checkout -b "${K8S_REPO_BRANCH}"
 
         # Update the internal dashboard image refs
@@ -45,7 +45,7 @@ runs:
         fi
 
         # Push changes and create a new merge request
-        git commit -m "Updating DRE container images"
+        git commit -m "Updating DRE container images from $DRE_REPO_BRANCH branch"
         git push \
           -o merge_request.create \
           -o merge_request.title="[nomrbot] - Updating DRE container images" \