Add pre-commit hook for validating release notes

- This is a pre-commit hook using `pre-commit` framework to validate release notes YAML files.
- The hook checks for correct structure, formatting and required fields in the `release-notes` directory.
- This ensures consistency in release notes before committing changes.
- Added release notes validation to the `make syntax-check` target

Ref: coreos#934 (comment)

.pre-commit-config.yaml

@@ -0,0 +1,9 @@
+repos:
+-   repo: local
+    hooks:
+    -   id: syntax-check
+        name: Syntax Check
+        entry: make syntax-check
+        language: system
+        types: [yaml, json]
+        files: ^(release-notes/.*\.yml$|streams/.*\.json$|updates/.*\.json$)

Makefile

@@ -1,7 +1,8 @@
-.PHONY: syntax-check
+.PHONY: syntax-check print-rollouts
+
 syntax-check:
 	@find streams updates -iname '*.json' | sort | xargs -n 1 python3 -c 'import json, sys; json.load(open(sys.argv[1]))'
+	@find release-notes -iname '*.yml' | sort | xargs -n1 python3 ci/check-release-notes.py
 
-.PHONY: print-rollouts
 print-rollouts:
 	@find updates -iname '*.json' -printf '%f\n' | cut -f1 -d. | sort | xargs ./rollout.py print