- `waitfornewblock` was previously not included in the public RPC
whitelist because it's reserved for testing and marked as hidden
in bitcoind.
- electrs changed its verbosity settings. `-vv` is now the best choice
for normal usage.
- bitcoind option `dataDirReadableByGroup` is now unused.
Because it can be valuable for other use cases and implementing
it is intricate, we're keeping it for now.
- test: keep `nc` connection open because otherwise the electrs
RPC server would now close the connection before sending a response.
