fix: proto-linter compliance (#55)

Adding some fixes for the proto linter, to 
re-enable it in CI and show it can be used to
validate AEP-compliant APIs.

.github/workflows/test.yml

@@ -32,8 +32,6 @@ jobs:
         run: |
           ./scripts/run-oas-linter.sh
 
-      # currently disabled due to api-linter bugs:
-      # - https://github.com/aep-dev/api-linter/milestone/1
-      # - name: run protobuf api-linter
-      #   run: |
-      #     ./scripts/run-api-linter.sh
+      - name: run protobuf api-linter
+        run: |
+          ./scripts/run-proto-linter.sh