[web] create Tunnelbroker session

Summary:
Create a diff that gathers the necessary data to establish a proper socket connection and begins to use the context.

Depends on D9607

Test Plan:
Use mock credentials (credentials that I manually added to Identity as a valid user) and verify if a session was created.

Reviewers: michal, bartek, tomek

Reviewed By: michal

Subscribers: ashoat, wyilio

Differential Revision: https://phab.comm.dev/D9609