feat: add flox envs command

[ysndr]

Allow to list all active environments using the envs sub command.

[ysndr]

@ghudgins @jennymahmoudi this is a very basic implementation using already existing active env formatting, let me know if this behaves the way you planned

[jennymahmoudi]

@ghudgins @jennymahmoudi this is a very basic implementation using already existing active env formatting, let me know if this behaves the way you planned

I think the acceptance criteria for this needs to be updated to be about all local environments, not just the active ones. I want to think about how this behaves with something like flox status which would tell you whether your env is active or not (and maybe all active envs) #752

I will update the ticket with AC this week.

[ysndr]

superseded by #1264