✨(back) check on document update if user can save it

When a document is updated, users not connected to the collaboration
server can override work made by other people connected to the
collaboration server. To avoid this, the priority is given to user
connected to the collaboration server. If the websocket property in the
request payload is missing or set to False, the backend fetch the
collaboration server to now if the user can save or not. If users are
already connected, the user can't save. Also, only one user without
websocket can save a connect, the first user saving acquire a lock and
all other users can't save.
To implement this behavior, we need to track all users, connected and
not, so a session is created for every user in the
ForceSessionMiddleware.

src/backend/impress/settings.py

@@ -291,6 +291,7 @@ class Base(Configuration):
         "django.middleware.common.CommonMiddleware",
         "django.middleware.csrf.CsrfViewMiddleware",
         "django.contrib.auth.middleware.AuthenticationMiddleware",
+        "core.middleware.ForceSessionMiddleware",
         "django.contrib.messages.middleware.MessageMiddleware",
         "dockerflow.django.middleware.DockerflowMiddleware",
         "csp.middleware.CSPMiddleware",
@@ -480,6 +481,7 @@ class Base(Configuration):
     SESSION_COOKIE_AGE = values.PositiveIntegerValue(
         default=60 * 60 * 12, environ_name="SESSION_COOKIE_AGE", environ_prefix=None
     )
+    SESSION_COOKIE_NAME = "docs_sessionid"
 
     # OIDC - Authorization Code Flow
     OIDC_CREATE_USER = values.BooleanValue(
@@ -659,6 +661,12 @@ class Base(Configuration):
         environ_prefix=None,
     )
 
+    NO_WEBSOCKET_CACHE_TIMEOUT = values.Value(
+        default=120,
+        environ_name="NO_WEBSOCKET_CACHE_TIMEOUT",
+        environ_prefix=None,
+    )
+
     # Logging
     # We want to make it easy to log to console but by default we log production
     # to Sentry and don't want to log to console.
@@ -853,15 +861,9 @@ class Development(Base):
     CSRF_TRUSTED_ORIGINS = ["http://localhost:8072", "http://localhost:3000"]
     DEBUG = True
 
-    SESSION_COOKIE_NAME = "impress_sessionid"
-
     USE_SWAGGER = True
-    SESSION_CACHE_ALIAS = "session"
     CACHES = {
         "default": {
-            "BACKEND": "django.core.cache.backends.dummy.DummyCache",
-        },
-        "session": {
             "BACKEND": "django_redis.cache.RedisCache",
             "LOCATION": values.Value(
                 "redis://redis:6379/2",