…257)

### Summary

Currently, on upload the attachments are loaded into memory (and then
copied a couple of times), which makes it impossible to upload video
files larger than a few hundred megabytes. With this change, the video
files are read using an `InputStream`, so the file is read from the
storage as needed.

### Other Information

- [ ] I have signed [Metabolist's Contributor License
Agreement](https://metabolist.org/cla)
- [x] The proposed changes are limited in scope to fixing bugs, or I
have discussed larger scope changes via email