chore(ci): add initial support for backport assistant

.github/workflows/backport-assistant.yml

@@ -0,0 +1,33 @@
+# This action creates downstream PRs for PRs with backport labels defined.
+# See docs here: https://github.com/hashicorp/backport-assistant
+
+name: Backport Assistant Runner
+
+on:
+  pull_request_target:
+    types:
+      - closed
+      - labeled
+
+jobs:
+  backport:
+    if: github.event.pull_request.merged
+    runs-on: ubuntu-latest
+    container: hashicorpdev/backport-assistant:0.2.3
+    steps:
+      - name: Run Backport Assistant for stable-website
+        # Update this to auto-merge when we have confidence in the process working and kill Circle
+        run: |
+          backport-assistant backport -merge-method=rebase
+        env:
+          BACKPORT_LABEL_REGEXP: "type/docs-cherrypick"
+          BACKPORT_TARGET_TEMPLATE: "stable-website"
+          GITHUB_TOKEN: ${{ secrets.ELEVATED_GITHUB_TOKEN }}
+      - name: Run Backport Assistant for release branches
+        # Update this to auto-merge when we have confidence in the process working and kill Circle
+        run: |
+          backport-assistant backport -merge-method=rebase
+        env:
+          BACKPORT_LABEL_REGEXP: "backport\/(?P<target>\\d+\\.\\d+)"
+          BACKPORT_TARGET_TEMPLATE: "release/{{.target}}.x"
+          GITHUB_TOKEN: ${{ secrets.ELEVATED_GITHUB_TOKEN }}