Allow passing fetcher/link options to delegateToSchema, transformSchema, and mergeSchemas

[yaacovCR]

This would allow removing makeRemoteExecutableSchema and a layer of delegation. It would also facilitate sharing a link/cache between microservices, although still possible with present architecture.

[yaacovCR]

Live in graphql-tools-fork v6.2.0

https://www.npmjs.com/package/graphql-tools-fork

Implemented in mergeSchemas and transformSchema as specification of option bag including schema and remote options instead of just schema.

Implemented differently within delegateToSchema as addition of executor and subscriber properties that can modify the execution method, and a delegateToRemoteSchema that sets these properties to send the remote graphql request instead of executing against the schema. This more generic solution also allows library users to set these options for local schemas, for example, if aiming to use a custom root value or default field/type resolver when executing locally.