RFC2046 allows the Content-Type field to have additional parameters
after the main type/subtype information (Section 1).
Following RFC4281, many applications put codec information inside
parameters in the Content-Type. This is especially common for formats
that support many codecs, such as Ogg (RFC5334, Section 4).
The `/api/audio/transcriptions` endpoint is currently rejecting files
that contain parameters in the Content-Type field with a bad request
error.
This commit changes the current check in order to accept any
Content-Type field that begins with a supported type/subtype as listed
in the `supported_filetypes` tuple.
Since Content-Type here is provided by the user, I believe this check
is meant to prevent honest mistakes, like posting a PDF to an audio
processing endpoint, not as a security measure against possibly
malicious use. Therefore, I think it's OK not to validate the rest of
the field.
Remove unnecessary `pathlib.Path` conversions. (CACHE_DIR and DATA_DIR)
Use `/` Path joining shorthand to ensure using platform specific Path separators (Windows: \\, Unix: /)
