Add a config file for dependabot

This allows us to set the separator used by dependabot
when setting the branch name. Otherwise, we end up with
branches that break our cloud build workflows

services/git-bridge/.github/dependabot.yml

@@ -0,0 +1,21 @@
+version: 2
+updates:
+  - package-ecosystem: "maven"
+    directory: "/"
+    schedule:
+      interval: "daily"
+
+    pull-request-branch-name:
+      # Separate sections of the branch name with a hyphen
+      # Docker images use the branch name and do not support slashes in tags
+      # https://github.com/overleaf/google-ops/issues/822
+      # https://docs.github.com/en/github/administering-a-repository/configuration-options-for-dependency-updates#pull-request-branch-nameseparator
+      separator: "-"
+
+    # Block informal upgrades -- security upgrades use a separate queue.
+    # https://docs.github.com/en/github/administering-a-repository/configuration-options-for-dependency-updates#open-pull-requests-limit
+    open-pull-requests-limit: 0
+
+    labels:
+      - "dependencies"
+      - "type:maintenance"