adk-python parity: support output schema with tools for LlmAgent

[jpallas]

See google/adk-python@af63567 and google/adk-python#701.

[jinnigu]

Hi @jpallas, thanks for raising this issue! I have created a PR: #603 to support this feature.

cc: @Poggecci Please help review.

[glaforge]

Should be fixed in #1074 in previous commits