Consider use of CodeFileLoader in graphql-config extensions

[Chnapy]

Consider use of CodeFileLoader in graphql-config extensions so pass most of literal-extract logic into graphql-config.

External doc:

• https://www.graphql-config.com/docs/library/extensions
• https://www.graphql-tools.com/docs/documents-loading
• https://www.graphql-tools.com/docs/graphql-tag-pluck

Related #6 #24

[Chnapy]

Closed by #22

Using CodeFileLoader with graphql-config not possible since this solution is schema-based (start from schema to documents), where TS compiler is script-based (start from script to schemas).