Add Mergify configuration for Dependabot

Add a mergify.yaml configuration file which automates the review and
merging of pull requests generated by Dependabot.

.github/mergify.yml

@@ -0,0 +1,69 @@
+---
+# When working with Dependabot and GitHub Actions, where those Actions can make
+# changes to documentation or code based on updates to the repository's
+# dependencies, it is always necessary for the pull requests to go though
+# multiple stagings using the force-integrations-run label. These rules take
+# this into account and allow those stages to be managed and triggered as
+# necessary.
+
+pull_request_rules:
+  # If the pull request was raised by Dependabot, and only Dependabot or GitHub
+  # Actions have make changes to the branch, then automatically approve if it's
+  # not in conflict with the base branch, and not closed.
+  - name: Automatic approval for Dependabot pull requests
+    conditions:
+      - 'author=dependabot[bot]'
+      - 'base=main'
+      - '#commits-behind=0'
+      - '-conflict'
+      - '-closed'
+      - or:
+          - 'commits[*].author==dependabot[bot]'
+          - 'commits[*].author==github-actions[bot]'
+    actions:
+      review:
+        type: APPROVE
+
+  # If a commit other than the initial commit is added to a pull request raised
+  # by Dependabot, and that commit author is GitHub Actions, and the last
+  # synchronised commit title starts with the word Syncing, then add the
+  # force-integrations-run label to trigger the GitHub Workflows for this
+  # commit
+  - name: Trigger force-integrations-run on GitHub Actions commits
+    conditions:
+      - 'author=dependabot[bot]'
+      - 'base=main'
+      - '#commits>1'
+      - 'commits[-1].author=github-actions[bot]'
+      - 'commits[-1].commit_message~=^Syncing'
+      - '#commits-behind=0'
+      - '-label=force-integrations-run'
+      - '-conflict'
+      - '-closed'
+      - not:
+          or:
+            - check-neutral~=^Remove Label
+            - check-pending~=^Remove Label
+            - check-success~=^Remove Label
+    actions:
+      label:
+        add:
+          - 'force-integrations-run'
+
+  # If the pull request was raised by Dependabot, it only has a linear history,
+  # it has been approved for merging into the main or master branches, and is
+  # neither in conflict with the main branch, fallen behind, nor the
+  # force-integrations-run label is still present, then automatically merge
+  # this request.
+  - name: Automatic merge for Dependabot pull requests
+    conditions:
+      - 'author=dependabot[bot]'
+      - 'base=main'
+      - 'linear-history'
+      - '#approved-reviews-by>=1'
+      - '-label=force-integrations-run'
+      - '-conflict'
+      - '-closed'
+    actions:
+      merge:
+        method: