Add buf protobuf linting

.gitlab-ci.yml

@@ -10,3 +10,12 @@ test:
     - dotnet tool restore
     - dotnet nuke Test
 
+protobuf-lint:
+  stage: test
+  image:
+    name: docker.io/bufbuild/buf:latest
+    entrypoint: [""]
+  script:
+    - cd api/
+    - buf ls-files
+    - buf lint