[Fix],Correct read in Jinja configuration and update docs of SupersetAppInitializer (#8908)

superset/app.py

@@ -81,7 +81,7 @@ class SupersetAppInitializer:
 
     def pre_init(self) -> None:
         """
-        Called after all other init tasks are complete
+        Called before all other init tasks are complete
         """
         wtforms_json.init()
 
@@ -90,7 +90,7 @@ class SupersetAppInitializer:
 
     def post_init(self) -> None:
         """
-        Called before any other init tasks
+        Called after any other init tasks
         """
         pass
 

superset/extensions.py

@@ -44,9 +44,7 @@ class JinjaContextManager:
         }
 
     def init_app(self, app):
-        self._base_context = self._base_context.update(
-            app.config["JINJA_CONTEXT_ADDONS"]
-        )
+        self._base_context.update(app.config["JINJA_CONTEXT_ADDONS"])
 
     @property
     def base_context(self):