fix warning so the user has a clear next step (#16751)

Author: nohalon

src/lightning_app/components/serve/auto_scaler.py

@@ -453,7 +453,9 @@ def _get_endpoint_info_page(self) -> Optional["APIAccessFrontend"]:  # noqa: F82
         try:
             from lightning_api_access import APIAccessFrontend
         except ModuleNotFoundError:
-            logger.warn("APIAccessFrontend not found. Please install lightning-api-access to enable the UI")
+            logger.warn(
+                "Some dependencies to run the UI are missing. To resolve, run `pip install lightning-api-access`"
+            )
             return
 
         if is_running_in_cloud():

src/lightning_app/components/serve/python_server.py

@@ -293,7 +293,9 @@ def configure_layout(self) -> Optional["Frontend"]:
         try:
             from lightning_api_access import APIAccessFrontend
         except ModuleNotFoundError:
-            logger.warn("APIAccessFrontend not found. Please install lightning-api-access to enable the UI")
+            logger.warn(
+                "Some dependencies to run the UI are missing. To resolve, run `pip install lightning-api-access`"
+            )
             return
 
         class_name = self.__class__.__name__