Make Polkadot support `--rpc-methods` param

[duktig666]

Parameter description

--rpc-methods <METHOD SET>
            RPC methods to expose. [default: auto] [possible values: auto, safe, unsafe]

Why support this parameter about --rpc-methods ?

I want to get some information about Polkadot for peerCount,currentBlock,highestBlock. If you want to get this information, I need to access the following RPC method:

• system_syncState

  {"jsonrpc":"2.0","result":{"startingBlock":0,"·":6321799,"highestBlock":10525440},"id":1}

• system_health

  {"jsonrpc":"2.0","result":{"peers":41,"isSyncing":true,"shouldHavePeers":true},"id":32}

  
  However, to implement the above functions, I need to use the following parameters:--rpc-methods=unsafe. But our system does not support this parameter at present.

Result

This configuration has been applied and verified in our project, which is feasible.