Relay v20 treats extend type in server schema as client extensions,
causing all mutation fields to have "text": null in generated artifacts.
Replace the cat-based schema concatenation with a merge script that
collects all extend type Mutation blocks and produces a single
type Mutation definition. The split graphql/ files remain the source
of truth for gqlgen; the merged schema.graphql is generated for Relay.
Signed-off-by: Émile Ré <emile@getprobo.com>
00b233aa03