Add eldctrumx websocket endpoint staked

[kampleforth]

websocat wss://electrumx.prod-utility-eks-us-west-2.staked.cloud:443

{"jsonrpc": "2.0", "method": "blockchain.headers.subscribe", "id": 0}
{"jsonrpc": "2.0", "result": {"hex": "000020203c4282d8c69d75dc19fd71d241a6c280f6d06bc79d0300000000000000000000ba17f8fb123f985d01ffbc3c7eafa4b37ead8dfae1bd6486966ac3f410f9d44db20e8264697e051757466427", "height": 793426}, "id": 0}

[pdyraga]

@nkuba Should we merge #3599 first or did you integrate-test it locally?

[nkuba]

@nkuba Should we merge #3599 first or did you integrate-test it locally?

I ran the tests locally.