Improve error experience from push

[JakeDawkins]

Originally from #108 (comment)

When a graph push or subgraph push fails, we don't really have any context beyond the plain text that studio returns. It looks like:

Error: Failed while pushing to Apollo Studio. To see a full printout of the schema attempting to push, rerun with `--log debug`

Caused by:
    encountered a GraphQL error, registry responded with: Could not parse as a GraphQL schema. Are you sure that your proposed schema is a parsable GraphQL schema?

It'd be nice to have a more custom error experience here, with more instructions

[lrlna]

@JakeDawkins do you think this is fixed with #275 ?

[JakeDawkins]

@lrlna I don't think so necessarily, but I also don't think we really need to work on this error state too much. I don't think we'll be able to return any more info about invalid schemas than what studio returns to us, so I'm fine with closing this

[lrlna]

Ok, let us close this then and revisit at a later date if necessary!