Create a Rake task to generate the GraphQL schema and generate types in vglist-frontend

[connorshea]

It should essentially automate the steps from the vglist-frontend README. We can just assume vglist-frontend is a sister directory to vglist.

- In your copy of the vglist Rails app, run bundle exec rake graphql:schema:dump to generate a dump of the GraphQL schema.
- Copy the newly-generated schema.graphql file to the vglist-frontend directory, probably with cp schema.graphql ../vglist-frontend.
- In vglist-frontend, run yarn run generate to regenerate the GraphQL types.