[docs] Add FETCH_LOG monitoring metrics to Fluss monitor-metrics doc (apache#1611)

Author: beryllw

website/docs/maintenance/observability/monitor-metrics.md

@@ -440,11 +440,13 @@ Some metrics might not be exposed when using other JVM implementations (e.g. IBM
     </tr>
     <tr>
       <td rowspan="7">
-          request_productLog
+          request_produceLog
           request_putKv
           request_lookup
           request_prefixLookup
           request_metadata
+          request_fetchLogClient
+          request_fetchLogFollower
       </td>
       <td>requestsPerSecond</td>
       <td>The total number of requests processed per second for each request type.</td>