File upload miscategorizes *.jfif files as application/octet-stream

### Expected Behavior

When uploading files, either as the entire request body or as a file inside a Multipart Form, *.jfif files should have the content header `image/jpeg` [at least according to W3C](https://www.w3.org/Graphics/JPEG/).

### Actual Behavior

Insomnia selects the generic Content-Type `application/octet-stream` instead. For files as the only body of a request we can override this in the **Headers** section, but when sending files as part of a Multipart Form, the Content-Type for individual files seems to be completely inaccessible.
```
> Accept: */*
> Content-Length: 81608

* TLSv1.2 (OUT), TLS header, Supplemental data (23):
* TLSv1.2 (OUT), TLS header, Supplemental data (23):
* TLSv1.2 (OUT), TLS header, Supplemental data (23):
* TLSv1.2 (OUT), TLS header, Supplemental data (23):

| --X-INSOMNIA-BOUNDARY
| Content-Disposition: form-data; name=""; filename="sample1.jfif"
| Content-Type: application/octet-stream
| ����JFIF



��C
```

### Reproduction Steps

1. Create a new POST request with a `Multipart Form`
2. Make one of the form parts a `File`
3. Select a *.jfif file to send
4. Send the request (you may need to expand the `Max timeline chunk size (KiB)` value to see the file's selected Content-Type

### Is there an existing issue for this?

- [X] I have searched the [issue tracker](https://www.github.com/Kong/insomnia/issues) for this problem.

### Additional Information

_No response_

### Insomnia Version

2023.5.8

### What operating system are you using?

Windows

### Operating System Version

Windows 10 Enterprise version 22H2

### Installation method

download from insomnia.rest

### Last Known Working Insomnia version

_No response_

Trace Insomnia's file-upload handling and extension-to-content-type mapping, starting with the multipart form path described in the reproduction steps. Reproduce the request with a .jfif file and verify that both a standalone upload and a multipart file part use image/jpeg instead of application/octet-stream.

Written by the indexing model from the issue text.