add-credential input field should support tab completion

[Jorge Castro]

The field to input the file name for a local json file in add-credential gets the job done, but it's kind of crude.

It would be nice if it supported tab completion and other things you'd expect, like the delete key, etc. Especially since google gave me a file with a huge filename:

    $ juju add-credential google
    credential name: jorge-juju
    select auth-type [jsonfile*, oauth2]: jsonfile
    file: /home/jorge/cloud-creds/client_secret_712944951979-7ehespmks8u1p4bv23psulvo1k4pkqh.apps.googleusercontent.com.json
    credentials added for cloud google

[Anastasia (anastasia-macmood)]

Arrow keys is the other addition to the list in the description.

[Anastasia (anastasia-macmood)]

I have found a bigger umbrella report which talks about Juju tab completion in prompts in general. I'll mark this is a duplicate since this needs to be addressed globally for all Juju commands rather than individually for credentials commands.