Update _index.md (#5871)

The new default for :
- `chunk_retain_period` is `0s`, not `30s`
- `chunk_idle_period` is `30m`, not `1h`
- `chunk_target_size ` is `1572864`, not `1048576`

According to https://grafana.com/docs/loki/v2.4/configuration/#ingester_config

docs/sources/upgrading/_index.md

@@ -206,9 +206,9 @@ present in your Loki config: `ingestion_rate_strategy`, `max_global_streams_per_
 
 | config | new default | old default|
 | --- | --- | --- |
-| chunk_retain_period | 30s | 0s |
-| chunk_idle_period | 1h | 30m |
-| chunk_target_size | 1048576 | 1572864 |
+| chunk_retain_period | 0s | 30s |
+| chunk_idle_period | 30m | 1h |
+| chunk_target_size | 1572864 | 1048576 |
 
 * chunk_retain_period is necessary when using an index queries cache which is not enabled by default. If you have configured an index_queries_cache_config section make sure that you set chunk_retain_period larger than your cache TTL
 * chunk_idle_period is how long before a chunk which receives no logs is flushed.