Proposal: rename --roles flag to --mode

[one000mph]

A small change like this could lessen confusion for new users. I'd like to be careful with the term "role" since an important feature of Teleport is the ability to assign user roles from in an access-control content. I think the name of the teleport --roles flag is a bit misleading as they describe the different services or modes that the teleport binary can run.

[benarent]

Thanks @one000mph , this is a good suggestion.

I can see how --roles can be confusing with RBAC roles , we mostly recommend that customers set roles via the Teleport.yaml, but I've found being explicit in the role/mode I start Teleport can be helpful ( I have found it i'm not explicit Teleport can start in all three 'roles/modes'.

I'll put this on the back burner, as CLI changes are more substantial but I'm currently doing a review of the CLI flags so it's come at a good time.

[one000mph]

Having just delved into Node Authorization and certificates I can see how the term "role" makes sense here, since nodes are given permissions within the system based on the --role flag. I still think that coming up with a different term might help with clarity so I'll leave this open for ideas.