[Agents Extension] Add a sample for creating an agent with existing code, using uv and pyproject.toml instead of requirements.txt

[trangevi]

This use case currently generates the following error:

ERROR: step "deploy-hr-agent" failed: deploying service hr-agent: failed deploying service 'hr-agent': agent deployment failed: [CodeError] hint: Consider enabling use of system TLS certificates with the --system-certs command-line flag | Exit code: 1 | Please review your uv.lock | More information: https://aka.ms/troubleshoot-python For troubleshooting, see https://aka.ms/hostedagents/tsg/code (request-id: 1c3234b0d43fd3f42418ce8e0cc0c03a)

This can be gotten past by adding "system-certs = true" to a uv.toml in the agent folder. It would be good to have an example of this kind of requirements install/management flow