feat: add rpc url to nwaku, persist rln tree in docker and ci

[adklempner]

Problem

Tests that run against cluster id 1 (The Waku Network) require running an nwaku node with a sepolia RPC url. When adding this parameter, the nwaku node will not be "ready" (/health returns status 200) until the RLN tree is synced. If starting from scratch, this process takes a long time (up to 5 minutes, and will only take longer as more blocks are mined on Sepolia).

Solution

Add a step to the CI that:

• checks if the rln_tree.db is stored as an artifact. If so, pull it.
• run an nwaku node in docker that mounts the rln_tree.db until the /health endpoint returns 200 (basically syncs the rln_tree to latest block on sepolia)
• store the synced rln_tree.db as an artifact

Notes

• Resolves #1914

Contribution checklist:

• [ ] covered by unit tests;
• [ ] covered by e2e test;
• [ ] add ! in title if breaks public API;