YSQL: Disable random warmup of connections in Connection Manager

Summary: This diff disables the random mode of warmup and allocation of connections when using Connection Manager, while keeping it only enabled for java tests.

Test Plan:
Jenkins: enable connection manager, all tests

Verified locally using test logs that random warmup is still enabled, and using a local cluster to verify that warmup mode is disabled by default for regular use

Reviewers: skumar, mkumar, devansh.saxena, vpatibandla, stiwary

Reviewed By: skumar

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D39488

java/yb-pgsql/src/test/java/org/yb/pgsql/BasePgSQLTest.java

@@ -351,6 +351,8 @@ protected void customizeMiniClusterBuilder(MiniYBClusterBuilder builder) {
       builder.enableYsqlConnMgr(true);
       builder.addCommonTServerFlag("ysql_conn_mgr_stats_interval",
         Integer.toString(CONNECTIONS_STATS_UPDATE_INTERVAL_SECS));
+      builder.addCommonTServerFlag("TEST_ysql_conn_mgr_dowarmup_all_pools_mode",
+        warmupMode.toString().toLowerCase());
       builder.addCommonTServerFlag("ysql_conn_mgr_superuser_sticky", "false");
     }
   }
@@ -665,12 +667,8 @@ void setConnMgrWarmupModeAndRestartCluster(ConnectionManagerWarmupMode wm) throw
       return;
     }
 
-    Map<String, String> tsFlagMap = getTServerFlags();
-    tsFlagMap.put("TEST_ysql_conn_mgr_dowarmup_all_pools_mode",
-      wm.toString().toLowerCase());
     warmupMode = wm;
-    Map<String, String> masterFlagMap = getMasterFlags();
-    restartClusterWithFlags(masterFlagMap, tsFlagMap);
+    restartCluster();
   }
 
   protected boolean isConnMgrWarmupRoundRobinMode() {

src/yb/yql/pggate/ybc_pggate.cc

@@ -99,7 +99,7 @@ DEFINE_UNKNOWN_bool(ysql_disable_server_file_access, false,
 
 DEFINE_NON_RUNTIME_bool(ysql_enable_profile, false, "Enable PROFILE feature.");
 
-DEFINE_test_flag(string, ysql_conn_mgr_dowarmup_all_pools_mode, "random",
+DEFINE_test_flag(string, ysql_conn_mgr_dowarmup_all_pools_mode, "none",
   "Enable precreation of server connections in every pool in Ysql Connection Manager and "
   "choose the mode of attachment of idle server connections to clients to serve their queries. "
   "ysql_conn_mgr_dowarmup is responsible for creating server connections only in "