Support envs BIBI_UPLOAD_URL and BIBI_BOOKSHELF_UPLOAD_URL?
Are configuration files enough?
BIBI_URL
might be considered better but it seems URL to read EPUB files by Bibi like https://s3.your-region.amazonaws.com/mybucket/bibi/
, but URL to upload like s3://mybucket/bibi
is intended here. So, I added _UPLOAD
.