Fix flask dependencies issue

Author: filippomc

infrastructure/common-images/cloudharness-flask/requirements.txt

@@ -3,6 +3,15 @@ Flask==1.1.2
 Flask-Cors==3.0.9
 flask-oidc==1.4.0
 Flask-Testing==0.6.1
-gunicorn
+gunicorn==20.1.0
+itsdangerous==2.0.1
+Jinja2==3.0.3
+jsonschema<4.0.0
+openapi-spec-validator==0.4.0
+pytest==4.6.11
+pytest-cov==3.0.0
+pytest-randomly==1.2.3
+sentry-sdk==0.14.4
+SQLAlchemy==1.4.32
 swagger-ui-bundle==0.0.8
 Werkzeug==2.0.3