feature(postgres) add pipelining support (#20986)

Co-authored-by: cirospaciari <6379399+cirospaciari@users.noreply.github.com>

src/sql/postgres/ConnectionFlags.zig

@@ -2,6 +2,8 @@ pub const ConnectionFlags = packed struct {
     is_ready_for_query: bool = false,
     is_processing_data: bool = false,
     use_unnamed_prepared_statements: bool = false,
+    waiting_to_prepare: bool = false,
+    has_backpressure: bool = false,
 };
 
 // @sortImports