tools (config): Disable caching by default:

Caching is currently broken, and some refactoring is planned. we disable it until it's
fixed.

libervia/backend/tools/config.py

@@ -357,8 +357,9 @@ class CommonSettings(ConfigOptions):
         default_factory=list, description="List of admin email addresses"
     )
     mutli_users: bool = Field(default=False, description="Enable multi-user support")
+    # FIXME: cache is temporarily disabled by default (it's broken)
     pubsub_cache_strategy: Literal["no_cache"] | None = Field(
-        default=None, description="PubSub cache strategy"
+        default="no_cache", description="PubSub cache strategy"
     )
     hosts: dict[str, dict | str] = Field(
         default_factory=dict,