Add possibility to set max db connections

Since it's an important part of a connection pool configuration, allow
to configure max db connections, that pool will open to a target db.
From this numbers several others (like default pool size, min pool size,
reserve) will be deduced, taking into account desired number of instances.

pkg/util/constants/pooler.go

@@ -11,5 +11,7 @@ const (
 	ConnectionPoolDefaultMemoryRequest = "100Mi"
 	ConnectionPoolDefaultMemoryLimit   = "100Mi"
 
-	ConnPoolContainer = 0
+	ConnPoolContainer            = 0
+	ConnPoolMaxDBConnections     = 60
+	ConnPoolMaxClientConnections = 10000
 )