[typescript-graphql-request] Add support for graphql-request's native batching solution.

**Is your feature request related to a problem? Please describe.**

graphql-request supports [batching](https://github.com/prisma-labs/graphql-request#batching), but it cannot be used with the sdk.

**Describe the solution you'd like**

The plugin should generate a batched version of the queries, e.g. `sdk.queryNameBatch` where the first parameter is an array instead of an object.

**Describe alternatives you've considered**

I can create a client directly by using `GraphQLClient` from `graphql-request` and call `client.batchRequests( [ { document: QueryDocumentFromGeneratedFile } ] )` but it's not ideal (I have to manually set the return type of the method).