park-api: errors on startup if config.secrets.yaml is missing

[hbruch]

Currently, park-api relies on external provisioning of etc/park-api/config.secrets.yaml.

If someone tries to use ipl-orchestration standalone,park-api-flask does not start successfully, as the missing config file is created as directory:

  File "/app/webapp/entry_point_gunicorn.py", line 8, in <module>
    app = launch()
  File "/app/webapp/app.py", line 36, in launch
    configure_app(app, testing=testing)
  File "/app/webapp/app.py", line 50, in configure_app
    config_loader.configure_app(app, testing)
  File "/app/webapp/common/config/config_loader.py", line 48, in configure_app
    app.config.from_file(config_secrets_path, safe_load)
  File "/usr/local/lib/python3.10/dist-packages/flask/config.py", line 296, in from_file
    with open(filename, "r" if text else "rb") as f:
IsADirectoryError: [Errno 21] Unable to load configuration file (Is a directory): '/app/config.secrets.yaml'

I suggest to

• assure that the file exists, e.g. via touch in the make init target
• document (or link to the documentation) the now needed configuration in the CHANGELOG
• provide some more setup instructions in the README.md