Support generated server side fragments

[ivan333m]

It would be so great if Hasura supports some kind of server side fragments. Auto-generated or created by user through UI. It allows the user to change set of fields in single place and do not duplicate field set in the code.

Example:

1. Fragment generated and stored on server side:

 fragment server_side_fragment on my_entity {
   id
   name
   valid_from
   valid_till
   version_id
}

2. Using server side fragment in all queries:

query getEntities() {
  my_entity(id: "7") {
     ...server_side_fragment
  }
}