Group dependabot docker updates

Allow dependabot to include multiple docker updates in a single PR
to reduce the number of PRs opened (reducing CI overhead) since we
usually want to update them all anyway, and there are a few duplicates
such as the git image used in both the release pipeline and import
resources feature.

.github/dependabot.yml

@@ -6,6 +6,10 @@ updates:
     schedule:
       interval: "weekly"
       day: "sunday"
+    groups:
+      all:
+        patterns:
+          - "*"
     labels:
     - "area/dependency"
     - "dependencies"