[lib] Bump invite link accept timeout

Summary:
Joining a community might be expensive and we should increase its timeout to match other, similar, operations. Extracted a const to make sure we're using the same timeout in all the related places.

https://linear.app/comm/issue/ENG-7924/improve-invite-link-join-timeout-handling

Test Plan: Flow

Reviewers: inka, atul

Reviewed By: inka

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11758