[FEATURE REQUEST] Better cli AutoComplete in bash shell and others shell

[Rockin2]

Is your feature request related to a problem? Please describe.
I began to use the salt.bash script to have autocomplete of the salt command in Bash. However, it is not complete. There is no autocompletion for pillars and states for example.

Describe the solution you'd like
A better autocompletion. I think Salt itself must have code for the autocomplete feature. Let the bash script be ultra simple and do all the work in Python in the Salt code. Maybe we can create a Autocomplete module in Salt. With that, it should be simple to add autocompletion to other shells like fish, zsh, etc.

Describe alternatives you've considered
Rewrite the bash script without modifying salt code. However, I think the bash script will be complicated and the support of others shells will not be simple.