[CQ] Add verify-csa bot experimentally to CQ

BUG=chromium:685561
NOTRY=true
TBR=danno@chromium.org, kjellander@chromium.org

Review-Url: https://codereview.chromium.org/2652653013
Cr-Commit-Position: refs/heads/master@{#42700}

infra/config/cq.cfg

@@ -45,6 +45,10 @@ verifiers {
         name: "v8_linux64_rel_ng_triggered"
         triggered_by: "v8_linux64_rel_ng"
       }
+      builders {
+        name: "v8_linux64_verify_csa_rel_ng"
+        experiment_percentage: 100
+      }
       builders { name: "v8_linux_arm64_rel_ng" }
       builders {
         name: "v8_linux_arm64_rel_ng_triggered"