feat(rover): rover subgraph check

[EverlastingBugstopper]

rover subgraph check ready to go. it pretty much copies exactly what the existing CLI does.

run the checks, print composition errors if they exist.

if no composition errors, iterate over check results and print a formatted table to stderr. if there are failures, count them and return an error so the CLI exits with a non-zero exit code.

user testing here for folks familiar with checks would be super great :)

[JakeDawkins]

as a potential future improvement, we could make a table of these errors similar to checks. Composition errors should always be in the format [Service] Type.field? -> Message so maybe we could parse out into two columns like location and message. But this is fine for now :)

[EverlastingBugstopper]

yeah, the way it prints it is as so:

 ERROR [films] Person -> A @key directive specifies a field which is not found in this service. Add a field to this type with @external.
 ERROR [films] Person -> A @key selects iddd, but Person.iddd could not be found
 ERROR [films] Person -> extends from people but specifies an invalid @key directive. Valid @key directives are specified by the originating type. Available @key directives for this type are:
        @key(fields: "id")
Error: Encountered 3 composition errors while composing the subgraph

i think if we wanted to print it like a table we'd want to have that data returned in separate fields by the API rather than trying to parse out these strings.