🔧(backend) add FRONTEND_CSS_URL env var

We added the `FRONTEND_CSS_URL` environment
variable. It will give the possibility to add a
css layer at runtime.

src/backend/core/api/viewsets.py

@@ -1689,6 +1689,7 @@ class ConfigView(drf.views.APIView):
             "CRISP_WEBSITE_ID",
             "ENVIRONMENT",
             "FRONTEND_THEME",
+            "FRONTEND_CSS_URL",
             "MEDIA_BASE_URL",
             "POSTHOG_KEY",
             "LANGUAGES",

src/backend/core/tests/test_api_config.py

@@ -19,6 +19,7 @@ pytestmark = pytest.mark.django_db
     COLLABORATION_WS_URL="http://testcollab/",
     CRISP_WEBSITE_ID="123",
     FRONTEND_THEME="test-theme",
+    FRONTEND_CSS_URL="http://testcss/",
     MEDIA_BASE_URL="http://testserver/",
     POSTHOG_KEY={"id": "132456", "host": "https://eu.i.posthog-test.com"},
     SENTRY_DSN="https://sentry.test/123",
@@ -39,6 +40,7 @@ def test_api_config(is_authenticated):
         "CRISP_WEBSITE_ID": "123",
         "ENVIRONMENT": "test",
         "FRONTEND_THEME": "test-theme",
+        "FRONTEND_CSS_URL": "http://testcss/",
         "LANGUAGES": [
             ["en-us", "English"],
             ["fr-fr", "Français"],

src/backend/impress/settings.py

@@ -411,6 +411,10 @@ class Base(Configuration):
         None, environ_name="FRONTEND_THEME", environ_prefix=None
     )
 
+    FRONTEND_CSS_URL = values.Value(
+        None, environ_name="FRONTEND_CSS_URL", environ_prefix=None
+    )
+
     # Posthog
     POSTHOG_KEY = values.DictValue(
         None, environ_name="POSTHOG_KEY", environ_prefix=None

src/frontend/apps/e2e/__tests__/app-impress/config.spec.ts

@@ -9,6 +9,7 @@ const config = {
   CRISP_WEBSITE_ID: null,
   COLLABORATION_WS_URL: 'ws://localhost:4444/collaboration/ws/',
   ENVIRONMENT: 'development',
+  FRONTEND_CSS_URL: null,
   FRONTEND_THEME: 'default',
   MEDIA_BASE_URL: 'http://localhost:8083',
   LANGUAGES: [