[Tunnelbroker] Add initial websocket connection support and connection map
Summary:
Add simple websocket implementation which can be used to easily onboard
keyserver support.
Part of:
Test Plan:
cd services/tunnelbroker cargo run
Reviewers: varun, bartek
Reviewed By: bartek
Subscribers: ashoat, tomek, atul
Differential Revision: https://phab.comm.dev/D7610