Add Sigchain-powered invite links

[adrastaea]

Description

Before we can sync a sigchain, we need to enable an invite flow which means that we must be able to create invites and share the invite secrets alongside other necessary connection info

Acceptance Criteria

1. Long lived invite created when the invite link is generated
2. Invite link includes invite secret
3. Invite link is displayed in “Add members” UI / QR code
4. Invite link is short enough to stay linkified / not be truncated in WhatsApp, Signal
5. Failing to generate LFAInviteLink will generate InviteLinkV1 (e2e test compatibility feature)
6. Test for generating valid invite link

[islathehut]

Marking for posterity:

• Maximum link length on Signal: 1600 (unofficial but user reported)
• Maximum link length on WhatsApp: 4096 (no link-specific link length but that is the message limit)