Add support for multipart file uploads

[SpaceSaver]

I just made a similar post on the server side, but I believe adding this would require changes to the app too. Perhaps the ability to select a max file size, or on the server dictate one that the app then respects? This is the issue on the server side that I opened: BlueBubblesApp/bluebubbles-server#622

The advantage of multipart file uploads is circumvention of arbitrary request size limits imposed by proxy services like Cloudflare. Cloudflare limits requests to 100MB in size.

[tneotia]

dupe of #2605

[tneotia]

wait this is actually saying something else nvm