Use Npgsql's new CloneWithAsync

Closes #3303

Author: roji

src/EFCore.PG/Storage/Internal/INpgsqlRelationalConnection.cs

@@ -22,5 +22,5 @@ public interface INpgsqlRelationalConnection : IRelationalConnection
     ///     any release. You should only use it directly in your code with extreme caution and knowing that
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
-    INpgsqlRelationalConnection CloneWith(string connectionString);
+    ValueTask<INpgsqlRelationalConnection> CloneWith(string connectionString, bool async, CancellationToken cancellationToken = default);
 }

src/EFCore.PG/Storage/Internal/NpgsqlDatabaseCreator.cs

@@ -208,7 +208,9 @@ private async Task<bool> Exists(bool async, CancellationToken cancellationToken
         var unpooledCsb = new NpgsqlConnectionStringBuilder(_connection.ConnectionString) { Pooling = false, Multiplexing = false };
 
         using var _ = new TransactionScope(TransactionScopeOption.Suppress, TransactionScopeAsyncFlowOption.Enabled);
-        var unpooledRelationalConnection = _connection.CloneWith(unpooledCsb.ToString());
+        var unpooledRelationalConnection =
+            await _connection.CloneWith(unpooledCsb.ToString(), async, cancellationToken).ConfigureAwait(false);
+
         try
         {
             if (async)

src/EFCore.PG/Storage/Internal/NpgsqlRelationalConnection.cs

@@ -226,9 +226,14 @@ public override Transaction? CurrentAmbientTransaction
     ///     any release. You should only use it directly in your code with extreme caution and knowing that
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
-    public virtual INpgsqlRelationalConnection CloneWith(string connectionString)
+    public virtual async ValueTask<INpgsqlRelationalConnection> CloneWith(
+        string connectionString,
+        bool async,
+        CancellationToken cancellationToken = default)
     {
-        var clonedDbConnection = DbConnection.CloneWith(connectionString);
+        var clonedDbConnection = async
+            ? await DbConnection.CloneWithAsync(connectionString, cancellationToken).ConfigureAwait(false)
+            : DbConnection.CloneWith(connectionString);
 
         var relationalOptions = RelationalOptionsExtension.Extract(Dependencies.ContextOptions)
             .WithConnectionString(null)