Make `RelationType.set_relates` return the created role

[james-whiteside]

Problem to Solve

Currently, RelationType.set_relates returns Promise[None]. This is pretty inconvenient, as a lot of the time we then want to perform further operations on the newly created role. Unlike the put methods for creating thing types, there is no parallel for roles, so they need to be gotten with RelationType.get_relates to continue operating on them like so:

message = transaction.concepts.put_relation_type("message").resolve()
message.set_relates(transaction, "sender").resolve()
message.set_relates(transaction, "recipient").resolve()
message_sender = response.get_relates(transaction, "sender").resolve()
message_recipient = response.get_relates(transaction, "recipient").resolve()

Proposed Solution

Make RelationType.set_relates return Promise[RoleType] instead of Promise[None], like so:

message = transaction.concepts.put_relation_type("message").resolve()
message_sender = message.set_relates(transaction, "sender").resolve()
message_recipient = message.set_relates(transaction, "recipient").resolve()