Go-ipfs: Add a config profile ls command

[Stebalien]

Currently, figuring out which profiles exist is a bit of a pain. It would be nice to have a config profile ls command that lists all the existing profiles.

Ideally, this would work by introspecting the list of profiles in repo/config/profile.go. However, to make that work, the Transformer functions there will need to be replaced with Profile structs:

type Profile struct {
    Description string
    Transformer func(c *Config) error
}

[preetsinojiya]

Will work on this!

[magik6k]

https://github.com/ipfs/go-ipfs/pull/4846/files sort of solves it already