feat: support jfif format

[ximing]

Details about the JFIF file format, please refer to https://docs.fileformat.com/image/jfif/

[broofa]

jshttp/mime-db#283

Edit: Better mime-db issue here: jshttp/mime-db#291

[broofa]

tldr: This module depends on mime-db. mime-db only pulls definitions from IANA, NGINX, or Apache... none of which list jfif as a file extension. Probably the best course of action here will be to go through IANA to update the JPEG registration and/or file a new one.