fix: every icon of the templates comes from the local icon cache

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.

webvirtcloud/test_icon_cache.py

@@ -0,0 +1,32 @@
+"""Every {% bs_icon %} of the templates is in the committed icon cache
+(BS_ICONS_CACHE). A missing one is fetched from the CDN when a page is
+rendered, or shown as an error where the server has no internet access."""
+
+import re
+import unittest
+from pathlib import Path
+
+from django.conf import settings
+
+BASE = Path(settings.BASE_DIR)
+CALL = re.compile(r"\{%\s*bs_icon\s+(.*?)\s*%\}")
+NAME = re.compile(r"""^['"]([^'"]+)['"]""")
+KWARG = re.compile(r"""(\w+)=['"]([^'"]*)['"]""")
+
+
+class IconCacheTestCase(unittest.TestCase):
+    def test_every_template_icon_is_cached(self):
+        cache = Path(settings.BS_ICONS_CACHE)
+        missing = []
+        templates = [*BASE.glob("templates/**/*.html"), *BASE.glob("*/templates/**/*.html")]
+        self.assertGreater(len(templates), 50)  # the globs still find the templates
+        for template in templates:
+            for args in CALL.findall(template.read_text(encoding="utf-8")):
+                name = NAME.match(args)
+                self.assertIsNotNone(name, f"{template}: icon name is not a literal: {args}")
+                kw = dict(KWARG.findall(args))
+                # the file name django-bootstrap-icons uses for its cache
+                cached = f"{name.group(1)}_{kw.get('size')}_{kw.get('color')}_{kw.get('extra_classes')}.svg".replace(" ", "_")
+                if not (cache / cached).exists():
+                    missing.append(f"{template.relative_to(BASE)}: {cached}")
+        self.assertEqual(missing, [])