Fix typo (#9217)

correct parameter is `leader_ca_cert_file`

website/pages/docs/configuration/storage/raft.mdx

@@ -140,7 +140,7 @@ storage "raft" {
   node_id = "node1"
   retry_join {
     leader_api_addr = "http://127.0.0.2:8200"
-    leader_ca_cer_file = "/path/to/ca1"
+    leader_ca_cert_file = "/path/to/ca1"
     leader_client_cert_file = "/path/to/client/cert1"
     leader_client_key_file = "/path/to/client/key1"
   }