fix: add missing default null value for connection_pool_config

Signed-off-by: Quoc Trung HOANG <[email protected]>

Author: ichbinfrog

modules/postgresql/variables.tf

@@ -525,4 +525,5 @@ variable "connection_pool_config" {
       value = string
     })), [])
   })
+  default = null
 }

modules/safer_mysql/variables.tf

@@ -436,4 +436,5 @@ variable "connection_pool_config" {
       value = string
     })), [])
   })
+  default = null
 }