feat: Add WebSockets support

[FrederikBolding]

Implements the rewritten SIP-20 to enable WebSocket support in Snaps.

WebSockets are supported via the WebSocketService which runs in the client and handles open WebSocket connections for the Snap. The Snap is notified of WebSocket events via onWebSocketEvent and is notified of open, close and message. Messages can also be sent from the Snap using snap_sendWebSocketMessage. Both string and binary payloads are allowed.

All of the new RPC methods are gated on endowment:network-access, which is also the permission required to expose onWebSocketEvent.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.21%. Comparing base (08bb538) to head (c0a0661).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3450      +/-   ##
==========================================
+ Coverage   98.18%   98.21%   +0.02%     
==========================================
  Files         399      404       +5     
  Lines       11136    11314     +178     
  Branches     1746     1763      +17     
==========================================
+ Hits        10934    11112     +178     
  Misses        202      202              

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[Mrtenz]

Note that this doesn't work on Node.js. Probably fine though.