Configure Dependabot for GitHub Actions (#606)

*Issue #, if available:* N/A

*Description of changes:*

This change configures Dependabot for Mountpoint's CSI Driver
repository. This will allow our dependencies to be updated on a
schedule, to avoid them getting too outdated and ensure we stay
relatively up-to-date.

For GitHub Actions, we allow each one to be updated separately. I feel
these are more challenging to review and will be best reviewed
individually. Note, this has been neglected and will launch a lot of
PRs. Initially, this change checks for updates daily and allows at most
1 PR to be open at a time. This is to manage the number of PRs
appearing. We should relax this later once we're in a better position.

This does not address Golang dependencies. Unfortunately, 0.x minor
releases are not treated as breaking changes and would introduce noise
to the repository. For now, we'll leave this out of scope.

This does not address Helm charts. Helm chart updates are currently
impacted by this bug in Dependabot:
dependabot/dependabot-core#11921. Once
resolved, I recommend we additionally configure Helm chart updates which
covers both Helm dependencies and the container images referenced.

By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

---------

Signed-off-by: Daniel Carl Jones <djonesoa@amazon.com>

Author: dannycjones

.github/dependabot.yml

@@ -0,0 +1,10 @@
+---
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    # Use limit of 1 PR, checked daily, to handle rush of updates.
+    # TODO: Remove, update to weekly once the wave is over.
+    open-pull-requests-limit: 1
+    schedule:
+      interval: "daily"