feat: Allow more audio media types, including FLAC

[rmunn]

Is your feature request related to a problem? Please describe.
As a follow-up to #1383, it seems to me that we should allow other file types to be uploaded. For example, the Free Lossless Audio Codec is a format that usually is 50-60% smaller than the .wav file of the same audio, but since it's a lossless codec, it can decompress into a .wav file that's byte-for-byte identical to the original. Also, if we're going to support the FLAC format (MIME type audio/flac, with audio/x-flac sometimes encountered even though it's non-standard), it would make sense to support the Ogg container format that FLAC files are often embedded in (MIME type audio/ogg and/or video/ogg).

Describe the solution you'd like
Add the .flac extension, and the audio/flac and audio/x-flac MIME types, to our file type whitelist in the uploadAudioFile method of LexUploadCommands. And have a discussion about whether to support other file types.

Describe alternatives you've considered
We don't necessarily need to do this urgently, as I'm not aware of anyone actually trying to upload FLAC or Ogg format files to Language Forge. Ogg is rarely used, for example. But since FLAC is lossless, and linguists often want to save their audio files in a lossless format, I wouldn't be surprised if at some point, someone were to decide to upload .flac files to save space. When (and if) that happens, it would be nice if we already have support in place for that format.

For other formats, it's more of a "well, why not?" case, even though I don't expect most of them to be used. E.g., https://developer.mozilla.org/en-US/docs/Web/Media/Formats/Containers#ogg says "While Ogg has been around for a long time, it has never gained the wide support needed to make it a good first choice for a media container. You are typically better off using WebM ..." in its advice on which media type to offer from your website. So I don't expect people to be beating down our door with .ogg files they want to upload. But if it's a commonly-used format, or a rarely-used format that would be useful for linguists' use cases (e.g. FLAC), there's probably not a good reason not to support it.