chore: add integration tests for rover introspect commands
Rover runs (and has run) two hard coded queries for introspection that are unlikely to change. There was a recent regression where these introspection queries weren't working for Apollo Server 4 because of some over-eager request rejections (https://github.com/apollographql/apollo-server/issues/7200).

In order to prevent regressions in the future, I propose spinning up an apollo server instance and running the following introspection queries against them as part of the test suite.

Query for `rover graph introspect` as a `curl` call

```console
$ curl https://countries.trevorblades.com -X POST -H "content-type: application/json" -H "user-agent: tool/0.0.0" -H "accept: */*" -H "accept: gzip, br" -H "host: countries.trevorblades.com" --compressed --data '{
  "variables": null,
  "query": "query GraphIntrospectQuery {\n  __schema {\n    queryType {\n      name\n    }\n    mutationType {\n      name\n    }\n    subscriptionType {\n      name\n    }\n    types {\n      ...FullType\n    }\n    directives {\n      name\n      description\n      locations\n      args {\n        ...InputValue\n      }\n    }\n  }\n}\n\nfragment FullType on __Type {\n  kind\n  name\n  description\n  fields(includeDeprecated: true) {\n    name\n    description\n    args {\n      ...InputValue\n    }\n    type {\n      ...TypeRef\n    }\n    isDeprecated\n    deprecationReason\n  }\n  inputFields {\n    ...InputValue\n  }\n  interfaces {\n    ...TypeRef\n  }\n  enumValues(includeDeprecated: true) {\n    name\n    description\n    isDeprecated\n    deprecationReason\n  }\n  possibleTypes {\n    ...TypeRef\n  }\n}\n\nfragment InputValue on __InputValue {\n  name\n  description\n  type {\n    ...TypeRef\n  }\n  defaultValue\n}\n\nfragment TypeRef on __Type {\n  kind\n  name\n  ofType {\n    kind\n    name\n    ofType {\n      kind\n      name\n      ofType {\n        kind\n        name\n        ofType {\n          kind\n          name\n          ofType {\n            kind\n            name\n            ofType {\n              kind\n              name\n              ofType {\n                kind\n                name\n              }\n            }\n          }\n        }\n      }\n    }\n  }\n}",
  "operationName": "GraphIntrospectQuery"
}'
```

Query for `rover subgraph introspect` as a `curl` call:

```console
$ curl https://countries.trevorblades.com -X POST -H "content-type: application/json" -H "user-agent: tool/0.0.0" -H "accept: */*" -H "accept: gzip, br" -H "host: countries.trevorblades.com" --compressed --data '{
  "variables": null,
  "query": "query SubgraphIntrospectQuery {\n    # eslint-disable-next-line\n    _service {\n        sdl\n    }\n}",
  "operationName": "SubgraphIntrospectQuery"
}'
```