[services] Configurable port

Summary:
Make the port that the server will listen on configurable.

https://linear.app/comm/issue/COM-95/make-the-port-configurable

Test Plan:
You can still build and run services the same way as up to this point. You can also specify port running something like:

cd services
yarn run-backup-server 12345
yarn run-tunnelbroker-server 12345

Reviewers: palys-swm, geekbrother, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, palys-swm, Adrian, atul, benschac, boristopalov

Tags: #aws_implement_services

Differential Revision: https://phabricator.ashoat.com/D2316