[lib] Extract a file with invite links constants

Summary:
We had an import cycle which blocked us from creating invite links from scripts. This diff moves the constants to a new place to break the cycle.

https://linear.app/comm/issue/ENG-8390/fix-creating-invite-links-from-scrips

Depends on D12425

Test Plan: Flow. Try to create a link from a script - there should be no error message about an uninitialized variable.

Reviewers: inka, ginsu, kamil

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12426