ci(config.yml): add prometheus client to circle ci for testing

.circleci/config.yml

@@ -57,6 +57,7 @@ jobs:
             pip install "pytest-mock==3.12.0"
             pip install python-multipart
             pip install google-cloud-aiplatform
+            pip install prometheus-client==0.20.0
       - save_cache:
           paths:
             - ./venv