[identity] [3/n] move websocket response functions to send.rs

Summary:
This moves websocket response functions to send.rs for organization purposes

Depends on D10804

Test Plan: cargo run server runs the websocket server successfully

Reviewers: varun, bartek

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10847