FontAwesome v6 and refactor the way we include icons

Summary:
Register icons from vue components that use them. The main reason for that
is to keep user.js as small as possible. Initially we saved 20KB, but
it would grow with new features added in the future.

Test Plan: `./phpunit --testsuite=Browser"

Reviewers: #hkccp_developers, vanmeeuwen

Reviewed By: #hkccp_developers, vanmeeuwen

Subscribers: #hkccp_developers

Differential Revision: https://git.kolab.org/D3526