feat: add ADK agent to be used in Tau2 bench

[selcukgun]

Provides a baseline ADK agent integration that can be registered in tau2 bench.

[happyhuman]

Please:
1- Run pylint on the python files and fix the linting issues first.
2- Follow the directory structures of other samples and create similar folders and subfolders for your agent (see https://github.com/google/adk-samples/tree/main/python/agents/academic-research for example)
3- Add a pyproject.toml and a .env.example file

[happyhuman]

A new script was added to the repo: ROOT/python/python-checks.sh

Please update your branch, and use this script to catch any lint issues. You can use it to check any formatting issues:

cd python
./python-checks.sh --run-lint agents/tau2-benchmark-agent
./python-checks.sh --run-black agents/ptau2-benchmark-agent
./python-checks.sh --run-isort agents/tau2-benchmark-agent

The lint issues need to be addressed and corrected. For black and isort, you may automatically fix them by running:

pip install black isort flake8   # In case the have not been already installed.
black agents/plumber-data-engineering-assistant
isort agents/plumber-data-engineering-assistant

Please address these before I review the PR.

[selcukgun]

Ran the python-checks.sh. It should be good for review now.