Add ability to send attachments in an interaction initial response

[tandemdude]

Summary

Adds the ability to pass attachments with create_initial_response

Checklist

• I have run nox and all the pipelines have passed.
• I have made unittests according to the code I have added/modified/deleted.

Related issues

[FasterSpeeding]

I'ma see if i can work on the rest server equivalent logic for this today

[FasterSpeeding]

Btw I do have a prototype impl of sending attachments on rest but i'm going to be waiting for discord to push a change they said they'd be pushing soon:tm: so if you remove the interaction server from this pr and switch out to handling de-duplicating the logic by moving out the payload building logic to a separate function instead of making the create_message logic work for create initial response this can be merged without the server logic

(and i'll do the server logic in another pr)

[FasterSpeeding]

Sry for the delay

[FasterSpeeding]

For a bit more specific detail on how I think this should be handled: instead of modifying _create_message to also handle initial response specific logic I think we would be better off taking the logic for building the message response payload and doing something like

def _build_message(self, message_body: JSONObjectBuilder, ...) -> Optional[URLEncodedFormBuilder]:

where _build_message should cover both edit and create semantics, and if it returns a URLEncodedFormBuilder then the calling logic should handle inserting the "payload_json" field before making the request

[tandemdude]

Tests are still a TODO but a pre-emptive review would be welcomed @FasterSpeeding 😉

[FasterSpeeding]

Meow

[hypergonial]

Woof