feat: RLN interaction front-end

[weboko]

Includes:

• generate membership from wallet;
• read Keystore;
• save to local storage;
• import / export Keystore;
• send messages by REST API;

Build on top of https://github.com/waku-org/js-waku-examples/pull/281 and eventually we should keep only one and possibly make it configurable enough to use for both cases.