[Cashtab] [Chronik Websocket Notifications] [Part 1] Connect to websocket

Summary:
T2447

Part 1 of a stacked diff for moving incoming transaction notifications to chronik websockets.

This diff

• Adds chronik-client and its dependencies
• Adds a chronik connection URL to the app settings object
• Implements websocket connection in useWallet.js, so that the connection function runs each time the user loads a new wallet

Test Plan:
npm start
Observe console.log statement matching the one in onConnect clause of initializeWebsocket function, "Chronik websocket connected"

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D11530