Migrate to gql templates for client queries/mutations/subscriptions

[b1zzu]

We should migrate to the gql template for the client queries/mutations/subscriptions generation in order to drop completely typescript transpile on runtime and the source module hack.

https://github.com/aerogear/graphback/blob/91c5b2cf57c95911de371f62558e908baf051d35/packages/graphback-codegen-client/src/ClientGenerator.ts#L26

graphql-testx/src/GraphbackClient.ts

Line 52 in 49b7e73

const client = await creator.createClient();