As a user, I'd like to define uniquely username, project name, and workflow definition name.

To enforce this, unique constraints should be implemented at the database level. When requests are made to the controller's endpoints, they should fail with an HTTP status code of 409 (Conflict) if the constraints are violated.

To ensure the uniqueness of the entity before creating it, a validation check needs to be performed. This check involves searching for the entity name to ensure it does not already exist in the system. Postgres already creates an index for unique key constraints.