Add assumeValidSDL config option

[jdolle]

To allow more flexibility, I've exposed graphql's assumeValidSDL option. (ref: https://github.com/graphql/graphql-js/blob/master/src/utilities/buildASTSchema.d.ts#L45)

I am intentionally using multiple directives and have a custom schema compiler. There are PRs to allow multiple directives (sangria-graphql/sangria#409 graphql/graphql-js#1541), but adding this option allows for more possibilities and more flexibility for peoples' schemas.

[jdolle]

Not sure why the check failed -- I ran test, build, build-website, and lint and they all passed.

[dotansimha]

@jdolle It's on our internal CI, just ignore it :)

Thanks for the PR, I'll review it soon

[dotansimha]

Thanks @jdolle

I'm not sure that adding it in the root is the right choice, because we might want to allow this only for specific inputs.
What do you think?

@ardatan @kamilkisiela

[jdolle]

Perhaps it would be better placed under the schema, similarly to the custom loader? I can make that change if so.

[ardatan]

@dotansimha This is something we should handle in graphql-toolkit's schema loaders. So we can move this to graphql-toolkit.

[dotansimha]

Sounds good, @jdolle , it can be under schema config.
@ardatan you are right, but we can merge it here and then later move it.

[ardatan]

#3147
This PR covers that functionality as an option to schema field like below;

schema:
  - your-schema-ptr:
      assumeValidSDL: true

[jdolle]

Closing since #3147 covers this. Thanks