django-bootstrap-icons serves icons from static/icon_cache and fetches a
missing one from the CDN while the page renders; a server without
internet access shows an error text instead of the icon.
- copy (Clone on the instance lists), envelope-open ("Lost OTP?" page)
and save (VM settings, network page) were not cached; they are now,
fetched with django-bootstrap-icons itself.
- The user and group lists asked for 'exclamation-triangle ' with a
trailing space, an icon that does not exist; the warning icon never
showed.
A test checks that every {% bs_icon %} in the templates has its cache
file; it fails on the previous files.
