🌱 Have dependabot track Dockerfile referenced images (#1908)

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: "