Provide default worker name and avoid duplicates

[pulkitsinghal]

Suggestion:

1. Running a command to create a worker results in an empty worker_name. By default, we should translate the "docker_image": "org/image" to be one of the following:
   1. "worker_name": "org/image" or
   2. "worker_name": "org_image" or
   3. "worker_name": "org-image" or
   4. "worker_name": "image"
2. When creating a worker with the same image repeatedly. We should decide if we want to avoid duplicates and enforce uniqueness based on docker_image or worker_name. Whatever we decide, we should enforce it.
   1. I vote for worker_name based uniqueness.
      1. I have tested that if I pass in the same worker name right now (not talking about empty or defaults anymore), it creates a new id for me every time in the DB, and we can improve upon that as it doesn't seem desirable.