Check out Postgraphile, it allows you to start off with introspection, then customise it with comments, then add custom bits in node. Both Hasura and Postgrap

Check out Postgraphile, it allows you to start off with introspection, then customise it with comments, then add custom bits in node. Both Hasura and Postgraphile also support schema stitching from what I know, so you should be able to extend it that way also (more complicated obviously)