ExportNode of MetaOperator should retrieve attributes recursively

Current ExportNode of MetaOperator retrieve attributes like this:

for n in self.operator.get_micro_graph().get_nodes():
            if n.type() == "Pad2D":
                self.attributes["padding"] = n.get_operator(
                ).attr.begin_end_borders
            if n.type() == "Conv2D":
                self.attributes["kernel_dims"] = n.get_operator(
                ).attr.kernel_dims
                self.attributes["stride_dims"] = n.get_operator(
                ).attr.stride_dims
                self.attributes["dilation_dims"] = n.get_operator(
                ).attr.dilation_dims

The goal of this issue is to allow to automatically retrieve attributes using a key like Conv2D{node_rank}:kernel_dims