[Feature] Expose utility to generate "full" API schema from entities GQL schema

Description

As it is, the only way to get the "true" GQL API schema is to deploy a subgraph and perform an introspection query. This is very painful for tooling and codegen purposes. It would be very nice to be able to generate the full schema locally from the "entities" schema.

I noticed this is relatively easy to isolate, as it is being done here: https://github.com/graphprotocol/graph-node/blob/252e9129588b0b022bcaf50bbe365287db18241b/graphql/examples/schema.rs

I'm actually in the process of creating a docker image that does exactly that. I basically cloned this repo, added a build target for that script and created a dockerfile that runs it, but it is not a very elegant solution. I'll still share it here once it's up in case someone else needs it.

I know this is more of a feature request for the CLI, but since the relevant code resides in this repo, and the CLI repo doesn't have a "Feature Request" template, I thought I'd open the issue here.

Are you aware of any blockers that must be resolved before implementing this feature? If so, which? Link to any relevant GitHub issues.

No response

Some information to help us out

• Tick this box if you plan on implementing this feature yourself.
• I have searched the issue tracker to make sure this issue is not a duplicate.

Start with graphql/examples/schema.rs, which the issue identifies as the existing schema-generation path, and trace how it derives a schema from the entities schema. Define the exposed utility's entry point and verify that it produces the full GQL API schema locally without deploying a subgraph or using introspection.