Ensure no positional args are set in stack command

[mrodm]

Fixes #942

This PR ensures that sub-commands from elastic-package stack do not accept positional arguments.

Example:

 $ elastic-package stack up -v -d --version 8.9.0 --services package-registry elasticsearch
Error: unknown command "elasticsearch" for "elastic-package stack up"

 $ elastic-package stack up -v -d --version 8.9.0 --services package-registry,elasticsearch
2023/08/28 16:28:10 DEBUG Enable verbose logging
2023/08/28 16:28:10 DEBUG Distribution built without a version tag, can't determine release chronology. Please consider using official releases at https://github.com/elastic/elastic-package/releases
Boot up the Elastic stack
...

[elasticmachine]

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• Commit: 7cdfe43

cc @mrodm