ci: Add Dependabot configuration for automatic dependency update checks

.github/dependabot.yml

+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://help.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    assignees:
+      - "Griefed"
+    labels:
+      - "dependencies"
+      - "github-actions"
+    target-branch: "master"
+
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    assignees:
+      - "Griefed"
+    labels:
+      - "dependencies"
+      - "npm"
+    target-branch: "master"
+
+  - package-ecosystem: "docker"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    assignees:
+      - "Griefed"
+    labels:
+      - "dependencies"
+      - "docker"
+    target-branch: "master"