[Deliverable] Implement basic RLN membership management module

[jm-clius]

Owner: AnonComms Zerokit-RLN

FURPS:

• F6. The basic RLN membership management module can register RLN memberships on-chain on behalf of a Logos module
• F7. The basic RLN membership management module stores and manages RLN keys for a Logos module
• F8. The basic RLN membership management module can operate as a client in the libp2p RLN membership allocation protocol

Checklist:

• Code: feat: rln membership management module + ui logos-lez-rln#18
• Dogfood: link to dogfooding session/artefact
• Docs: links to README.md or other docs