Add subgraph list command

[JakeDawkins]

This PR adds the subgraph list command, showing a table of all subgraphs, their routing urls and info about when they were last updated. We also print a url to the studio page where someone can go see these services and their respective schemas

UPDATED:

todo:

• use frontendUrlRoot in stdout printing to direct to studio

[EverlastingBugstopper]

This is coming together nicely! I think it'll be super useful. If we ever end up making graph list a thing, and someone doesn't provide a graph ref argument for subgraph list we could recommend running graph list or maybe even run it for them to give them a list of acceptable inputs.

When I ran the command for the first time on one of my federated graphs, I got this table:

+--------+-------------+--------------------------+
| Name   | Routing Url | Last Updated             |
+--------+-------------+--------------------------+
| people |             | 2020-12-18T18:29:14.795Z |
+--------+-------------+--------------------------+
| films  |             | 2020-12-18T18:28:59.734Z |
+--------+-------------+--------------------------+

I think having N/A in the service url if there isn't one would be a nice touch, in addition to formatting the Last Updated time a bit nicer.

---

I could also argue for a bit less verbose output by default, with an option to show this expanded table, so the output would look more like this (kinda like typical bash programs output sequential lines):

people
films

[lrlna]

I had two small things, and an even smaller nit. So close though!