Example CLI built on gfw-common, without Beam

[tomaslink]

PIPELINE-4673 · Stacked on #18 (merge that first).

Summary

Replaces the template's plain sys.argv entry point with an example CLI built on gfw-common, so new projects start from the standard pattern. No Beam: gfw-common is installed without extras, so the template also suits services.

Layout (as in pipe-anchorages)

src/python_app_template/
  cli/main.py                 # gfw-common CLI; registers commands; --labels shared by all
  cli/commands/hello.py       # Command: name, description, options → builds the config, calls its pipeline
  pipelines/hello/config.py   # HelloConfig(PipelineConfig): name, times (+ labels)
  pipelines/hello/main.py     # run(config: HelloConfig): the logic
config/hello/sample.yaml      # example configuration file

• python-app-template hello --name GFW --times 2 --labels environment=development, or -c config/hello/sample.yaml. Command-line arguments override the config file, and the config file overrides the defaults.
• HelloConfig inherits PipelineConfig (labels, from_namespace) and extends its validation (times >= 1).
• run() receives the typed config, not the CLI's SimpleNamespace: the command converts the CLI input at the edge (HelloConfig.from_namespace), so run has a typed signature that mypy checks, and other callers (DAGs, scripts, tests) build a validated HelloConfig directly. This differs from pipe-anchorages, where run converts the namespace itself; the template is meant to be the reference going forward.
• Tests: the command with run mocked (defaults, options, config file precedence), the configuration and the logic as plain functions.
• README: how to use the CLI, a config file example, and the new modules and config/ directory.

init_project.py: rename every Python file of the package and the tests

It only renamed a fixed list of files, so the new modules that import the package by name would have broken after renaming (reproduced: 6 files kept python_app_template). It now renames every .py file under src/<package>/ and tests/ (except its own tests, which use the template's name on purpose), and requirements-test.txt, whose compiled comments name the package.

Note

gfw-common doesn't ship a py.typed marker, so mypy treats its classes as Any; subclassing them under strict mypy needs # type: ignore[misc]. Follow-up: add py.typed to gfw-common.

Verification

• pytest: 18 passed, 100% coverage; flake8, ruff, black, mypy, codespell: clean.
• make docker-build && make docker-test: 11 passed (the image excludes init_project's tests). The production image runs python-app-template hello, and doesn't include apache_beam (148 MB).
• python init_project.py my-service on a copy: its 18 tests pass, my-service hello -c config/hello/sample.yaml greets twice, and the only remaining python-app-template strings are the links to the shared contributing guide.

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