Update shell tab completion for exercism cli

[nywilken]

What this does?

The Bash and Zsh tab completion files being shipped with the latest release reference subcommands that no longer exist. This changes updates the shell completion files with references to all of the implemented commands in Exercism v2.

** Note ** auto Bash completion generation in Cobra was looked into but it appears that Cobra requires a bit of configuration for each command we would want to generate bash completions for so I am going with manual update at this time.

How to test?

1. Follow the shell completion file install steps outlined here
2. Test tab completion for bash or zsh (exercism <tab>)
3. Verify list of commands as tab completion options

exercism
configure     -- Writes config values to a JSON file.
download      -- Downloads and saves a specified submission into the local system
help          -- Shows a list of commands or help for one command
open          -- Opens a browser to exercism.io for the specified submission.
submit        -- Submits a new iteration to a problem on exercism.io.
troubleshoot  -- Outputs useful debug information.
upgrade       -- Upgrades to the latest available version.
version       -- Outputs version information.
workspace     -- Outputs the root directory for Exercism exercises.

resolves #666

[nywilken]

@kytrinyx I confirmed completion is working as expected for zsh and bash on my end. But I would like to confirm that the changes work as expected on another user's machine before merging. Let me know if you have time to take a look.

[kytrinyx]

This works on my machine!

[Atulkmr]

@kytrinyx why do we need additional configuration to get tab completion? Can't it come out of the box?

[kytrinyx]

@Atulkmr I'm not sure I understand your question. The binary that we deliver cannot control your machine's path. The extra configuration is what tells your machine about the options for the binary.