openBalena: document and warn/prevent execution of unsupported CLI commands

[pdcastro]

There are CLI commands that only work with balenaCloud, not openBalena, because they rely on functionality that is only available in the former. Examples are balena push <appName> (which relies on the balenaCloud builder) and balena os download (which relies on the API's /download endpoint, not available on openBalena.

Currently this not sufficiently documented and execution of those CLI commands may fail with unintuitive error messages like "No such version for the device type" or "Internal Server Error". The help output of those commands should indicate openBalena compatibility, and execution should be prevented if openBalena can be somehow detected (perhaps by checking the API URL?).

[jellyfish-bot]

[georgiats] This issue has attached support thread https://jel.ly.fish/0e4c9faa-e542-4314-a35a-59d5c5c9fa59

[jellyfish-bot]

[anujdeshpande] This issue has attached support thread https://jel.ly.fish/18a9d888-1962-4a8f-a847-7f8bcffc539a