Schema caching broken for multiple schemas since 2.1.0

[patsissons]

Issue Labels

• has-reproduction
• feature
• docs
• blocking
• good first issue

The current schema caching implementation (added in #137) currently prevents a multi-project (aka multi-schema) configuration as it keys caching on the eslint configuration, whereas schema resolution is dependent on the path to the GraphQL file being linted.

We can fix this by caching the schemas and the graphql configuration (along with the other cached elements) and instead of returning the cache entry directly, compose the cache hit into a result based on the file path being linted.