require sign-off in commits

Signed-off-by: Ryan Richard <richardry@vmware.com>

.pre-commit-config.yaml

@@ -1,23 +1,30 @@
 # This is a configuration for https://pre-commit.com/.
 # On macOS, try `brew install pre-commit` and then run `pre-commit install`.
+default_install_hook_types: [ pre-commit, commit-msg ]
+default_stages: [ pre-commit ]
 repos:
-    - repo: https://github.com/pre-commit/pre-commit-hooks
-      rev: v5.0.0
-      hooks:
-          # TODO: find a version of this to validate ytt templates?
-          # - id: check-yaml
-          #   args: ['--allow-multiple-documents']
-          - id: check-json
-          - id: end-of-file-fixer
-          - id: trailing-whitespace
-          - id: check-merge-conflict
-          - id: check-added-large-files
-          - id: check-byte-order-marker
-          - id: detect-private-key
-          - id: mixed-line-ending
-    - repo: local
-      hooks:
-          - id: validate-copyright-year
-            name: Validate copyright year
-            entry: hack/check-copyright-year.sh
-            language: script
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v5.0.0
+    hooks:
+      # TODO: find a version of this to validate ytt templates?
+      # - id: check-yaml
+      #   args: ['--allow-multiple-documents']
+      - id: check-json
+      - id: end-of-file-fixer
+      - id: trailing-whitespace
+      - id: check-merge-conflict
+      - id: check-added-large-files
+      - id: check-byte-order-marker
+      - id: detect-private-key
+      - id: mixed-line-ending
+  - repo: local
+    hooks:
+      - id: validate-copyright-year
+        name: Validate copyright year
+        entry: hack/check-copyright-year.sh
+        language: script
+      - id: check-signoff
+        name: Check for Signed-off-by
+        entry: 'grep -q "^Signed-off-by: "'
+        language: system
+        stages: [ commit-msg ]