[docs] Add Metrics Updates to the Upgrade Notes v0.8 (#1698)

Author: swuferhong

website/docs/maintenance/operations/upgrade-notes-0.8.md

@@ -27,6 +27,27 @@ Please also upgrade your Flink deployment to **Java 11 or above**. All Flink ver
 
 We have updated the report level for some metrics and also removed some metrics, this greatly reduces the metrics amount and improves the performance.
 
-The following metrics are removed: TODO
-
-The following metrics are changed: TODO
+The following metrics are removed:
+
+- `fluss_tabletserver_table_bucket_inSyncReplicasCount` - Removed as redundant. Use `fluss_tabletserver_underReplicated` instead
+- `fluss_tabletserver_table_bucket_log_size` - Removed as improvement. Use `fluss_tabletserver_table_bucket_logicalStorage_logSize` instead
+- `fluss_tabletserver_table_bucket_kv_snapshot_latestSnapshotSize` - Removed as improvement. Use `fluss_tabletserver_table_bucket_logicalStorage_kvSize` instead
+
+The following metrics are changed:
+
+- The reporting level has been shifted from the `tableBucket` level to the `tabletserver` level:
+  - `fluss_tabletserver_table_bucket_underMinIsr` to `fluss_tabletserver_underMinIsr`
+  - `fluss_tabletserver_table_bucket_underReplicated` to `fluss_tabletserver_underReplicated`
+  - `fluss_tabletserver_table_bucket_atMinIsr` to `fluss_tabletserver_atMinIsr`
+  - `fluss_tabletserver_table_bucket_isrExpandsPerSecond` to `fluss_tabletserver_isrExpandsPerSecond`
+  - `fluss_tabletserver_table_bucket_isrShrinksPerSecond` to `fluss_tabletserver_isrShrinksPerSecond`
+  - `fluss_tabletserver_table_bucket_failedIsrUpdatesPerSecond` to `fluss_tabletserver_failedIsrUpdatesPerSecond`
+  - `fluss_tabletserver_table_bucket_log_flushPerSecond` to `fluss_tabletserver_logFlushPerSecond`
+  - `fluss_tabletserver_table_bucket_log_flushLatencyMs` to `fluss_tabletserver_logFlushLatencyMs`
+  - `fluss_tabletserver_table_bucket_kv_preWriteBufferFlushPerSecond` to `fluss_tabletserver_kvFlushPerSecond`
+  - `fluss_tabletserver_table_bucket_kv_preWriteBufferFlushLatencyMs` to `fluss_tabletserver_kvFlushLatencyMs`
+  - `fluss_tabletserver_table_bucket_kv_preWriteBufferTruncateAsDuplicatedPerSecond` to `fluss_tabletserver_preWriteBufferTruncateAsDuplicatedPerSecond`
+  - `fluss_tabletserver_table_bucket_kv_preWriteBufferTruncateAsErrorPerSecond` to `fluss_tabletserver_preWriteBufferTruncateAsErrorPerSecond`
+- Correction addresses reporting errors in metric names by changing the `table` level metric prefix from `fluss_tabletserver_table__` (used a double underscore (__)) to `fluss_tabletserver_table_`. 
+  - The affected metrics are all metrics with [Scope: tableserver, infix: table](docs/maintenance/observability/monitor-metrics.md#tablebucket)
+  - For example, change `fluss_tabletserver_table__messagesInPerSecond` to `fluss_tabletserver_table_messagesInPerSecond`.