[Tunnelbroker] Make uri format more flexible

Summary:
For connecting to remote services, the uri holds a lot of
information (user, password, exchange, port, protocol).
Instead of trying to quantify all of the arguments, just
allow for the entire uri to be passed to tunnelbroker.

Part of https://linear.app/comm/issue/ENG-3715

Depends on D8178

Test Plan:

(cd services/tunnelbroker && RUST_LOG=debug cargo run -- --amqp-uri <remote uri> &)

(cd services/commtest && cargo test --test tunnelbroker_integration_test)

Reviewers: varun, bartek

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8214