Add file type filtering support for command options and file uploads

[KiloOscarSix]

https://docs.discord.com/developers/change-log#filter-file-types-in-file-uploads-and-attachment-options

Open Questions:

1. I went with an array of strings to best mirror the docs, but an Enum of Image, Video, Audio, Extension(String) could be argued for.
2. I'm not a fan of the:

Cow::Owned(
                file_types.into_owned().into_iter().map(|f| f.into_owned().into()).collect(),
            ),

but kinda ties into point one with how we want the api to look.

[meditationmind]

Overall looks fine to me. Could merge this as is, but I've noted a few docs nitpicks below, to make things more consistent with our own docs.

Also, successfully tested both slash commands and modals, and I can PR the slash changes to Poise once this is merged.