Mint: add websockets for quote updates

[callebtc]

This PR implements the new Websocket NUT (cashubtc/nuts#98) on the client and on the server side. At the client side, we use a websocket connection to the mint. This connection sends json-rpc commands with a predefined set of commands. For now, these are only subscription commands. These allow you to subscribe to state updates of melt and mint quotes, and proofs. Clients can subscribe with filters to quote id's (for mint and melt quotes), or to the Proof.Y point (for ecash).

Whenever there is an update, the mint looks up all subscriptions for any of the triggered filters and sends updated Bolt11MintQuote or Bolt11MeltQuote and ProofState objects to the client.

Todos:

• NUT NUT-17: WebSocket state updates nuts#98
• Test websocket responses
• Test CLI invoice
• Do not return unnecessary fields in notification