add websocket to websocket diagnostic channels

[KhafraDev]

Fixes #4081

This might be a breaking change? undici:websocket:open is now published after the open event is emitted (similar to the current close channel behavior), before it was published before. Also in the opening event, extensions and protocol are now equivalent to their WebSocket.prototype versions, which means that they are now '' instead of null when empty.

[KhafraDev]

If it is a semver-major change, I'll throw in the changes to socket_error too. I was hoping it wouldn't be breaking, but looking at it now it probably is.

[mcollina]

why is it breaking? The object only had an additive change. Is there a major change in behavior?

[KhafraDev]

extensions and protocol were both already in the opening channel, but now when not present, they will be an empty string rather than null. It does also change the order of when the opening event is fired, but this isn't as important, but still potentially noticeable if you had something along the lines of:

const events = []
const ws = new WebSocket('ws://localhost')

diagnosticsChannel.subscribe('undici:websocket:open', () => events.push('dc open'))
ws.addEventListener('open', () => events.push('ws open'))

console.log(events) 
// before: ['dc open', 'ws open']
// after: ['ws open', 'dc open']

[mcollina]

I'd say we ship and revert if we broke anyone.