### Description
This small PR improves the representation of an endpoint method from `Text` to an enum of the supported methods. Additionally, it cleans some of the instances defined on surrounding types (such as Postgres-specific instances on Endpoint types).
Due to a name conflict, this makes `RQL.Types.Endpoint` impossible to re-export from `RQL.Types`, which in turn forces several other modules to import it explicitly, which I think is fine since we want to ultimately get rid of `RQL.Types`.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/3965
GitOrigin-RevId: 33869007d0d818ddf486fb61d1f6099f9dad7570