[hotfix][docs] Fix broken variable ${FLUSS_QUICKSTART_FLINK_VERSION}

Author: wuchong

website/docs/maintenance/observability/quickstart.md

@@ -146,7 +146,7 @@ services:
   #end
   #begin Flink cluster
   jobmanager:
-    image: fluss/quickstart-flink:${FLUSS_QUICKSTART_FLINK_VERSION}
+    image: fluss/quickstart-flink:1.20-$FLUSS_VERSION_SHORT$
     ports:
       - "8083:8081"
     command: jobmanager
@@ -159,7 +159,7 @@ services:
     volumes:
       - shared-tmpfs:/tmp/paimon
   taskmanager:
-    image: fluss/quickstart-flink:${FLUSS_QUICKSTART_FLINK_VERSION}
+    image: fluss/quickstart-flink:1.20-$FLUSS_VERSION_SHORT$
     depends_on:
       - jobmanager
     command: taskmanager

website/docs/streaming-lakehouse/overview.md

@@ -1,4 +1,5 @@
 ---
+sidebar_label: "Lakehouse Overview"
 sidebar_position: 1
 ---