feat: add graphql-tag support

[codeflyer]

Add support for schema generated by graphql-tag

Why is this an important feature?

To integrate tools that help to organise the project

(Eg.)

    const {loadFiles} = require('@graphql-tools/load-files')
    
    const schema = await loadFiles(
      path.resolve(__dirname, '../modules/**/*.graphql')
    )

    const resolvers = (await loadFiles(
      path.resolve(__dirname, '../modules/**/resolvers.js')
    )).reduce((acc, resolver) => {
      Object.entries(resolver).forEach(([key, value]) => {
        if(!acc[key]) {
          acc[key] = {}
        }

        acc[key] = {...acc[key], ...value}
      })

      return acc
    }, {})

[mcollina]

lgtm