RFC: "Welcome to Rover" on first command run

[EverlastingBugstopper]

Most of our commands require authentication! Maybe when we run any rover command while unauthenticated, we shouldn't even print like it's an error! Let's just welcome them to Rover:

$ rover subgraph fetch mygraph-i-know-exists > mygraph.sdl
Hi! I'm Rover, it looks like you're new here.

To authenticate, please head on over to https://studio.apollographql.com to grab your API key, and then run `rover config profile auth`.

[JakeDawkins]

Ah yeah! I love that. Rather than making an http request and printing out something ugly, we could definitely print a friendlier message first

A future improvement could be to somehow automatically run config auth when another command that needs auth is run

like:

$ rover subgraph fetch mygraph-i-know-exists > mygraph.sdl
Hi! I'm Rover, it looks like you're new here.

This command requires you be authenticaed with Apollo Studio!
Go to https://studio.apollographql.com/user-settings and create a new Personal API Key.

Copy the key and paste it into the prompt below.
> 

[JakeDawkins]

I'll tackle this first message though, just as a quick improvement :)