[keyserver] change function names for getting clients to be more intuitive

Summary:
i also added back a module that we made dead code for some reason in https://phab.comm.dev/D8820 ... we definitely need this function so i think it was a mistake. i should've reviewed this more carefully before commandeering the diff.

Depends on D9472

Test Plan: cargo build, also called the function i added back from js and confirmed it still worked as expected

Reviewers: bartek, michal

Reviewed By: bartek

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9473