feat(cli) support extra packages in cloud deployments

[sylvesterkaczmarek]

Link to Issue or Description of Change

• Closes Enable common folder ouside of adk-agent for code reusability #4980

Problem

Agent Engine supports --extra_packages, but Cloud Run and GKE deployments do not. Agents that share local Python packages therefore need duplicated code or custom deployment steps.

Solution

• Add a repeatable --extra_packages option to adk deploy cloud_run and adk deploy gke.
• Share package-staging logic across Agent Engine, Cloud Run, and GKE.
• Stage each file or directory at the build root, copy it to /app/<basename>, and keep /app on PYTHONPATH.
• Preserve missing-path and destination-conflict validation.
• Leave generated deployment output unchanged when the option is not used.

Testing Plan

• Added regression tests.
• Relevant tests pass.

pytest tests/unittests/cli/utils/test_cli_deploy_to_cloud_run.py tests/unittests/cli/utils/test_cli_deploy.py tests/unittests/cli/utils/test_cli_tools_click.py tests/unittests/cli/test_cli_tools_click_option_mismatch.py -q

190 passed, 1 xfailed in 5.94s

The tests cover CLI forwarding, file and directory staging, generated Dockerfile instructions, existing Agent Engine behaviour, and Click option consistency.

All applicable pre-commit hooks passed.

Manual E2E

Not run against Cloud Run or GKE because that requires cloud credentials and billable resources. Unit tests build and inspect the exact deployment context and Dockerfile.

Checklist

• I have read the CONTRIBUTING document.
• I have self-reviewed this change.
• I have added regression tests.
• Relevant tests pass locally.
• I have deployed the generated image to Cloud Run or GKE.
• This change has no downstream dependencies.

Additional context

The option semantics match the existing Agent Engine flag so projects can use one package layout across all supported deployment targets.