[keyserver] Construct a new TunnelbrokerSocket when one closes

Summary:
This resolves ENG-4924, and should address ENG-7318 as well.

Depends on D11391

Test Plan: I let the connection go away when my laptop went to sleep, and confirmed it was recreated after it was woken up

Reviewers: kamil, marcin

Reviewed By: kamil

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D11392