Support making an arbitrary HTTP request that returns an event stream

It would be nice if the plugin can support making an arbitrary HTTP request which returns an event stream response instead of just making a GET request to / in the _start_request method:

Example:

POST https://api.openai.com/v1/chat/completions

with headers

[
  "Content-Type: application/json",
  "Authorization: Bearer <token here>"
]

with body

{
  "stream": true,
  "messages": [{"role": "user", "content": "what is godot engine"}],
  "model": "gpt-4o-mini"
}