WS Client support for CLI

[AnnaShaleva]

Is your feature request related to a problem? Please describe.

@532910 is always frustrated when he can't run neo-go query height with WS RPC server endpoint.

Suggestion is to add WS Client support to CLI.

Describe the solution you'd like

options.GetRPCClient may return interface instead of *rpcclient.Client and make an internal switch over http[s]:// and ws[s]:// to create either http or a web-socket client. The draft is in https://github.com/nspcc-dev/neo-go/tree/wss-height, the only thing we need is to move all methods required by CLI from RPC client to interface.

Describe alternatives you've considered

Leave everything as is.