WIP: Allow the ApplyBfgObjectMapStream client to signal EOF explicitly

Unlike a unidirectional stream, gRPC doesn't allow the send part of a bidirectional stream to be closed by the client, so there's no built-in way to signal completion from client to server.

To get around this, add an eof boolean to the RPC's request message. This can be set on the final message sent by the client (whether it sends 1, 2, or 100 messages) to indicate that the whole file has been sent.

WIP for now since I'm not certain we want to take this approach.