added dependabot.yml for version updates (#31)

What
Adding base config for dependabot.yml, which enables automatic PRs for dependency version updates through Dependabot. This base config sets version updates to run on a weekly schedule, groups PRs for version updates according to major vs minor/patch updates, and sets max PRs that Dependabot can create for version updates per package-ecosystem.

Why
To enable using the latest package versions, and provide a way to customize Dependabot security updates PRs.

.github/dependabot.yml

@@ -0,0 +1,41 @@
+version: 2
+updates:
+  - package-ecosystem: "gomod"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "sunday"
+      time: "02:00"
+    open-pull-requests-limit: 2
+    groups:
+      minor-and-patch:
+        applies-to: version-updates
+        update-types:
+        - "patch"
+        - "minor"
+      major:
+        applies-to: version-updates
+        update-types:
+        - "major"
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "sunday"
+      time: "02:00"
+    open-pull-requests-limit: 2
+    groups:
+      all-actions:
+        applies-to: version-updates
+        patterns: [ "*" ]
+  - package-ecosystem: "docker"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "sunday"
+      time: "02:00"
+    open-pull-requests-limit: 2
+    groups:
+      all-docker:
+        applies-to: version-updates
+        patterns: [ "*" ]