websockets: Add `reason`, `code` and `wasClean` fields for `close` event

[etodanik]

Brief summary

MDN documentation for this event:
https://developer.mozilla.org/en-US/docs/Web/API/WebSocket/close_event

It's very important information to know the closure code and reason when a remote websocket closes connection.

k6 version

latest

OS

all

Docker version and image (if applicable)

No response

Steps to reproduce the problem

Get a weboscket server closure, and check if those fields exist

Expected behaviour

Those fields should exist and be populated

Actual behaviour

The fields don't exist

[codebien]

Hey @etodanik, I agree with the reported issue. Would you like to contribute by directly opening a pull request?

[etodanik]

Yes, I can contribute