[lib] Modify link verification to call the proper keyserver

Summary:
This diff allows calling any keyserver to check if a link is valid.

https://linear.app/comm/issue/ENG-5423/join-a-community-on-a-given-keyserver

Depends on D10206

Test Plan: Check if clicking an invite link opens a modal on web. Also checked if providing an explicit keyserver id works.

Reviewers: michal, bartek, rohan, inka

Reviewed By: inka

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D10290