rover supergraph fetch

[lrlna]

Description

It seems like Studio now has an API to do a supergraph fetch. We should consider replicating the same command in Rover to align with our graph and subgraph commands.

[EverlastingBugstopper]

The supergraphSdl field in the API is nullable, I'm guessing this is the case when composition errors occur. Do we want to return the latest composition error when attempting to fetch supergraph sdl? I'd.. assume we'd actually want this call to always return what's currently running on the gateway, and if the most recent composition publish has failed, maybe we should return the latest one to succeed?

[ndintenfass]

I think not. Probably should be an error state that no supergraph schema was found (maybe that error could link to Studio? Or you think it should inline any errors??)

[EverlastingBugstopper]

IMO there should likely be a separate field we can query that isn't necessarily mostRecentCompositionPublish, but instead mostRecentSuccessfulCompositionPublish, which would always return the most recent valid composed supergraphSdl.

i'd imagine folks would want to use this to update the schema that their gateway is using, and it wouldn't be super great if that just.. broke every time composition breaks, given the frequency with which that occurs.

we figured it out