feature request: add rpc similar to 'getblockchaininfo'

[octobocto]

I'm very interested in this info about the thunder chain:

./bitcoin-cli -rpcuser=user -rpcpassword=password -signet getblockchaininfo
{
  "chain": "signet",
  "blocks": 175556,
  "headers": 175556,
  "bestblockhash": "000000c5d2633c341dec64931ef46dc0523029030761fb0a9695e7bb2e1cbf96",
  "initialblockdownload": false,
  "size_on_disk": 94034954,
}

imo we can remove get-best-sidechain-block-hash, and replace it with get-blockchain-info