chore: Enable dependabot monthly updates (#234)

Monthly should be often enough for this project, we can cover security
updates separately.

I have ignored k8s.io packages as they should match what crossplane-runtime
uses.

Author: chlunde

.github/dependabot.yml

@@ -0,0 +1,19 @@
+version: 2
+updates:
+- package-ecosystem: gomod
+  directories:
+    - "/"
+  schedule:
+    interval: monthly
+  commit-message:
+      prefix: "chore: "
+  ignore: # Handled via the crossplane-runtime, this should ensure we don't run into compatibility issues
+    - dependency-name: "github.com/crossplane/crossplane-tools"
+    - dependency-name: "sigs.k8s.io/*"
+    - dependency-name: "k8s.io/*"
+- package-ecosystem: "github-actions"
+  directory: "/"
+  schedule:
+      interval: "monthly"
+  commit-message:
+      prefix: "chore: "