clientinfo: reduce length of client correlator

Summary: Length of 8 still gives 218,340,105,584,896 possible values, and will reduce space usage by 50%.

Reviewed By: quark-zju

Differential Revision: D67045388

fbshipit-source-id: a524ed603913c6be8c07c8e5ec34606bffb6a666

eden/scm/lib/clientinfo/src/request_info.rs

@@ -192,7 +192,7 @@ impl ClientRequestInfo {
         } else {
             thread_rng()
                 .sample_iter(Alphanumeric)
-                .take(16)
+                .take(8)
                 .map(char::from)
                 .collect()
         }