Add enum renaming ability to federated services.

[JacksonKearl]

TODO:

• Update CHANGELOG.md* with your change (include reference to issue & this PR)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

*Make sure changelog entries note which project(s) has been affected. See older entries for examples on what this looks like.

[JacksonKearl]

I question if the entire addResolversToSchema function isn't just a half-baked reimplementation of https://github.com/apollographql/graphql-tools/blob/master/src/generate/addResolveFunctionsToSchema.ts in graphql-tools. In particular my hacky implementation of renaming enums seems to be more thoughtfully implemented in https://github.com/apollographql/graphql-tools/blob/master/src/transforms/ConvertEnumValues.ts. Thoughts on if we should be pulling in graphql-tools and using its implementation?

[JacksonKearl]

Superseded by #1345