Support multiple GraphQL schemas

[salmankhilji]

I fail to see how the build.yaml file can support more than a single schema. In my simple command line app, I need to fetch a list of my repos from both GitLab and GitHub. How can I add multiple schemas to a single project?

Discord discussions for #ferry suggest to merge the schemas. However, with GitLab and GitHub being so closely related, there are conflicts with the schemas. For example:

GitLab has:

type Repository {
  ...
}

Whereas, GitHub has:

type Repository implements Node & PackageOwner & ProjectOwner & RepositoryInfo & Starrable & Subscribable & UniformResourceLocatable {
  ...
}

I suppose I could create two separate packages, each containing a its own build.yaml and a schema file, and then have my CLI app depend on the two packages. However, having to split a simple app into multiple packages seems an overkill due to this restriction.