Allow loading schema from SDL definition file as well as JSON

[Tabby]

If passing a path to a file with a name that ends in ".graphql" or ".graphqls" (matching the filenames used in
graphql-ruby), attempt to load the schema from that file assuming it's a schema definition rather than a JSON schema.

[jesstice]

Is there anything that can be done to help move this PR along? 🙏 This is something our team would benefit from as we have introspection disabled for our graphql server.

[Tabby]

Is there anything that can be done to help move this PR along? 🙏 This is something our team would benefit from as we have introspection disabled for our graphql server.

Knowing it would be helpful for someone else is a pretty good incentive to make time to finish it :)
Tests all pass locally now, and it tests loading a GraphQL schema SDL from both a string and from a file

➜  graphql-client git:(allow-loading-schema-from-sdl-definition) rake test
Run options: --seed 26501

# Running:

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Finished in 1.468751s, 115.7446 runs/s, 437.1061 assertions/s.

170 runs, 642 assertions, 0 failures, 0 errors, 4 skips

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