As a user, instead of keeping raw variables (which may be secrets) in my workflows, I would like to be able to reference a secret using " {{ secrets.SECRET_NAME }}".

PRD:

1. New screen in the settings page, that allows one to CRUD tenant secrets.
2. New API that utilizes SecretManagerFactory.get_secret_manager to CRUD secrets in the backend
3. Load relevant workflow secrets to context_manager to allow reference in a workflow