[Deliverable] Implement RLN membership management in nwaku library

[chair28980]

Owner: nwaku

Feature: RLN Membership Management

FURPS:

• F1. Can generate RLN credentials.

• F2. Can insert RLN membership in smart contract, with accompanying deposit.

• F3. Can extend RLN membership on smart contract.

• F4. Can withdraw deposit from smart contract.

• F5. Membership credentials are encrypted by default on local disk.

• U1. RLN membership details can be exported and imported.

• U2. Deployment details (address, chain id) are persisted by library and in exports.

• R1. Import and exports are interoperable across all implementations.

• S2. library can be used in Go applications; available on pkg.go.dev.

• S3. library can be used in Rust applications; import via git path.

• +2. Available for Linea Sepolia Testnet contracts.

Checklist:

• Specs: link to specs and/or API definition
• Code: link to GitHub issues/PRs/Epic
• Dogfood: link to dogfooding session/artefact
• Docs: links to README.md or docs.waku.org (TBD)