Set up clang-format in CI

ci/checkformat.gitlab-ci.yml

@@ -0,0 +1,11 @@
+checkformat:clangformat:
+  stage: checkformat
+  image: ubuntu:23.10
+  only:
+    - merge_requests
+  allow_failure: true
+  before_script:
+    - apt-get update -y
+    - apt-get install -y --no-install-recommends git clang-format-17
+  script:
+    - git clang-format-17 --diff --commit ${CI_MERGE_REQUEST_DIFF_BASE_SHA}