Humanize the byte size error on community image upload

[fenekku]

Package version (if known): 13.x (version compatible with InvenioRDM 12)

Describe the bugs

The file size and file size limit shown on the UI when uploading a too big community picture is not human-friendly.

It should be:

or at least make the display of size consistent with the rest of the UI and human friendly.

The error message doesn't go away once an appropriate picture is uploaded.

It should go away then.

Steps to Reproduce

1. Go to '/communities//settings'
2. Click on 'Upload new picture'
3. Upload a picture bigger than 1MB
4. See error