planner: add tidb_enable_binding_usage (#21946)

Author: hawkingrei

system-variables.md

@@ -2090,6 +2090,15 @@ Assume that you have a cluster with 4 TiDB nodes and multiple TiKV nodes. In thi
 - Default value: `OFF`
 - This variable controls whether to enable the deprecated batch-dml feature. When it is enabled, certain statements might be split into multiple transactions, which is non-atomic and should be used with care. When using batch-dml, you must ensure that there are no concurrent operations on the data you are operating on. To make it work, you must also specify a positive value for `tidb_batch_dml_size` and enable at least one of `tidb_batch_insert` and `tidb_batch_delete`.
 
+### tidb_enable_binding_usage <span class="version-mark">New in v9.0.0</span>
+
+- Scope: GLOBAL
+- Persists to cluster: Yes
+- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No
+- Type: Boolean
+- Default value: `ON`
+- This variable controls whether to collect the usage statistics of SQL plan bindings. When it is set to `ON`, TiDB writes the usage statistics of SQL plan bindings to the `mysql.bind_info` table every six hours.
+
 ### tidb_enable_cascades_planner
 
 > **Warning:**