feat(bitcoin): add OnFinality public Bitcoin RPC endpoint

[josealoha666]

Summary

Add a new public Bitcoin RPC endpoint to explorer-metadata:

• https://bitcoin.api.onfinality.io/public

Why

We need more working public BTC RPC options to improve resilience and failover.
This endpoint is currently responding correctly to standard Bitcoin JSON-RPC methods.

Validation (tested)

Endpoint tested successfully with:

• getblockcount
• getbestblockhash
• getblockchaininfo

Result was consistent with other working public endpoints at test time.

Candidate metadata

• Provider: OnFinality
• URL: https://bitcoin.api.onfinality.io/public
• Network: Bitcoin Mainnet (btc)
• Type: Public RPC
• Status: Working (as of test date)

Notes

Please include this endpoint in the BTC RPC list used by OpenScan metadata so it can be surfaced in Explorer RPC testing/selection flows.