specifying the output directory for generated type files

[briandennis]

With the splitting of graphqlgen.ts into several files (as per https://github.com/prisma/graphqlgen/issues/115) the function of the output setting in graphqlgen.yml needs to be updated.

Currently, it's used to specify a single output file which all types will be placed into:

output: ./src/generated/graphqlgen.ts  # all types go here

resolver-scaffolding:
  output: ./src/generated/tmp-resolvers/ # scaffolded resolvers go in this directory

Minimally, we could update this to specify a directory which the type files will be placed into:

output: ./src/generated/types 

resolver-scaffolding:
  output: ./src/generated/tmp-resolvers/

On the other hand, this may also be a good opportunity to set up some reasonable defaults and behavior for output path configuration. For example, often times it's probably enough to only specify a "namespace" for the output (e.g. ./src/generated/graphqlgen/) and implicitly write type files and resolver scaffolds to subfolders therein.

[schickling]

I'd suggest the following minimal change output: ./src/generated/graphqlgen.ts to output: ./src/generated/graphqlgen/. For now, I suggest putting all the files in one folder (maybe an additional index.ts file?).