Update changelog and deprecated config checker

CHANGELOG.md

@@ -62,6 +62,7 @@
 * [10959](https://github.com/grafana/loki/pull/10959) **slim-bean** introduce a backoff wait on subquery retries.
 * [11121](https://github.com/grafana/loki/pull/11121) **periklis** Ensure all lifecycler cfgs ref a valid IPv6 addr and port combination
 * [10650](https://github.com/grafana/loki/pull/10650) **matthewpi** Ensure the frontend uses a valid IPv6 addr and port combination
+* [11665](https://github.com/grafana/loki/pull/11665) **salvacorts** Deprecate and flip `-legacy-read-mode` flag to `false` by default.
 
 #### Promtail
 

docs/sources/setup/upgrade/_index.md

@@ -165,6 +165,7 @@ This new metric will provide a more clear signal that there is an issue with ing
 | `querier.tsdb-max-query-parallelism`                   | 128         | 512         | - |
 | `query-scheduler.max-outstanding-requests-per-tenant`  | 32000       | 100         | - |
 | `validation.max-label-names-per-series`                | 15          | 30          | - |
+| `legacy-read-mode`                                     | false       | true        | Deprecated. It will be removed in the next minor release. |
 {{% /responsive-table %}}
 
 #### Write dedupe cache is deprecated

tools/deprecated-config-checker/checker/checker_test.go

@@ -39,6 +39,7 @@ var (
 	}
 
 	expectedConfigDeprecates = []string{
+		"legacy-read-mode",
 		"ruler.remote_write.client",
 		"index_gateway.ring.replication_factor",
 		"storage_config.bigtable",

tools/deprecated-config-checker/deprecated-config.yaml

@@ -13,6 +13,7 @@
 #       _msg: "Use tsdb (preferred) or boltdb-shipper instead."
 #
 # Note that even though the configs in schema_config takes a list, here we specify the deprecated fields for each item in the list.
+legacy-read-mode: "Legacy read SSD mode is deprecated and will be eventually removed. Use the new read and backend targets."
 
 ruler:
   remote_write:

tools/deprecated-config-checker/test-fixtures/config.yaml

@@ -1,4 +1,5 @@
 auth_enabled: false
+legacy-read-mode: true
 
 server:
   http_listen_port: 3100