Implement Bodywork Deployment Delete

[Marios85]

"As an ML Engineer I want to be able to delete a deployment"

Implement a CLI command to delete a namespace (effectively kubectl delete ns project-name)

N.B. We need to update the docs to make it clear that if a user has specified a specific namespace to deploy to in the Bodywork YAML then this will be the name they have to give to the CLI or they will need to specify this as a parameter (would make the usage more consistent).

[AlexIoannides]

Change this to:

delete project_namespace

i.e. delete absolutely f*cking everything. Maybe double-check with the user first?