Added custom completions for loco and cargo loco commands

[andreystepanov]

Sharing custom completions I've written for myself with the community, especially those interested in Loco framework (It’s Like Ruby on Rails, but for Rust).

At this point it already auto-completes:

• environment (based on config/*.yaml filenames)
• task names (currently based on src/tasks/*.rs filenames)
• scheduler job names/tags (parsed from scheduler section of config/*.yaml, and it's aware of current --environment flag)
• model fields, after you typed field: and then pressed Tab key (field:uuid, field:string!, field:tstz! etc.)
• template names (for cargo loco generate override subcommand)
• and others

[fdncred]

Thanks