Collection posters cannot have filenames with UTF-8 characters

[cjcolvar]

Steps to reproduce:

1. Create a collection
2. Click Upload Poster
3. Choose a image file with a filename with UTF-8 characters (e.g. きた!.jpg)

Expected Behavior

Image file should be uploaded and stored as the collection poster image

Actual Behavior

Avalon raises an error: incompatible character encodings: ASCII-8BIT and UTF-8

[joncameron]

Notes: Active Storage was fine, but the reading back and rendering of the file is most likely the issue here.

[joncameron]

Tested and working: https://avalon-dev.dlib.indiana.edu/admin/collections/fb4948403