Add dependabot config (#87)

* Add dependabot config

.github/dependabot.yaml

@@ -0,0 +1,19 @@
+version: 2
+updates:
+# Create PRs for github.com/gardener/gardener dependency updates
+- package-ecosystem: gomod
+  directory: /
+  schedule:
+    interval: daily
+  open-pull-requests-limit: 5
+  allow:
+  - dependency-name: "github.com/gardener/gardener"
+# Create PRs for golang version updates
+- package-ecosystem: docker
+  directory: /
+  schedule:
+    interval: daily
+- package-ecosystem: docker
+  directory: /.test-defs
+  schedule:
+    interval: daily

.github/workflows/run_make_tidy_on_gardener_updates.yaml

@@ -0,0 +1,31 @@
+name: Run Make Tidy on Gardener Updates
+on:
+  push:
+    branches:
+    - dependabot/go_modules/github.com/gardener/gardener*
+permissions: write-all
+jobs:
+  run:
+    name: Run make tidy
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: actions/setup-go@v3
+      with:
+        go-version-file: go.mod
+
+    - name: Make tidy
+      run: make tidy
+    - name: Commit changes
+      run: |
+        # Exit early if there is nothing to commit. This can happen if someone pushes to the dependabot's PR (for example has to adapt to a breaking change).
+        if [[ -z $(git status --porcelain) ]]; then
+          echo "Nothing to commit, working tree clean. Exiting..."
+          exit 0
+        fi
+
+        git config user.name gardener-robot-ci-1
+        git config user.email [email protected]
+        git add .
+        git commit -m "[dependabot skip] make tidy"
+        git push origin