Add remove_credential() to Controller class

[leopaul36]

Description

The Controller class has a handy add_credential() method. It would be nice to also be able to delete credentials using a Controller instance.

Urgency

It would save from a weird workaround

Code I'd Like to Run

controller = Controller()
await controller.connect(controller_name=controller_name)
await controller.remove_credential(name=credential_name, cloud=cloud)