salt-api 3006+ needs additional configuration to work

[Erwin Dondorp]

Is your feature request related to a problem? Please describe.
See https://docs.saltproject.io/en/latest/topics/releases/3006.0.html
Each API subset must now individually be enabled

Describe the solution you'd like
Document what to add to the configuration.

Additional context
The full list of clients is:

netapi_enable_clients:
  - local
  - local_async
  - local_subset
  - runner
  - runner_async
  - ssh
  - wheel
  - wheel_async

some are not (yet) needed for SaltGUI

[Erwin Dondorp]

added first warning to documentation

[Erwin Dondorp]

only local, local_async, runner and wheel are needed for SaltGUI