Add flatten to logs_subscribe commitment (#13861)

Currently, commitment for `logs_subscribe` must be specified using the
non-flattened form in JSON, ie `{"commitment":{"commitment":"max}}`.
This brings the commitment in line with documentation.

(cherry picked from commit 6203d1c94c)

Co-authored-by: Jon Cinque <jon.cinque@gmail.com>

client/src/rpc_config.rs

@@ -82,6 +82,7 @@ pub enum RpcTransactionLogsFilter {
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct RpcTransactionLogsConfig {
+    #[serde(flatten)]
     pub commitment: Option<CommitmentConfig>,
 }