🌱 Have dependabot track Dockerfile images

Configure dependabot to create PRs when the images
we use in the `Dockerfile` have a newer version.  This
allows us to reference specific container images and
be automatically notified of newer versions.

Supports: #1883

CI added in #1907 will run against the PRs dependabot
will open for `Dockerfile` changes.  This will allow
us to have confidence that the update will be successful.

Signed-off-by: Scott J Dickerson <sdickers@redhat.com>

.github/dependabot.yml

@@ -9,3 +9,10 @@ updates:
     allow:
       - dependency-name: "@patternfly/*"
         dependency-type: "direct"
+
+  - package-ecosystem: docker
+    directory: /
+    schedule:
+      interval: daily
+    commit-message:
+      prefix: ":seedling: "