chore: update Dependabot configuration (#17)

* chore: add CODEOWNERS file to define repository ownership

* chore: update Dependabot configuration

- remove deprecated `reviewers` field
- add GitHub Actions monthly check

Author: panz3r

.github/CODEOWNERS

@@ -0,0 +1,7 @@
+# Each line is a file pattern followed by one or more owners.
+
+# These owners will be the default owners for everything in
+# the repo. Unless a later match takes precedence,
+# @panz3r will be requested for review when someone 
+# opens a pull request.
+*       @panz3r

.github/dependabot.yml

@@ -10,13 +10,14 @@ updates:
     directory: "/"
     schedule:
       interval: monthly
-    reviewers:
-      - "panz3r"
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: monthly
 
   - package-ecosystem: "npm"
     directory: "/"
     schedule:
       interval: weekly
       day: tuesday
-    reviewers:
-      - "panz3r"