[SNOW-1747456] Remove side effects from command registration

[sfc-gh-pjob]

Pre-review checklist

• I've confirmed that instructions included in README.md are still correct after my changes in the codebase.
• I've added or updated automated unit tests to verify correctness of my new code.
• I've added or updated integration tests to verify correctness of my new code.
• I've confirmed that my changes are working by executing CLI's commands manually on MacOS.
• I've confirmed that my changes are working by executing CLI's commands manually on Windows.
• I've confirmed that my changes are up-to-date with the target branch.
• I've described my changes in the release notes.
• I've described my changes in the section below.

Changes description

• Introduced CliAppFactory, which wraps all callback definitions. Thanks to that, callbacks and commands are not registered globally but only within an instance of CliAppFactory. The factory exposes create_or_get_app method.
• Removed global AppContextHolder in favour of get_click_context method exposed by CliAppFactory. Click context was and still is needed in tests traversing command tree (like docs generation tests).
• Simplified commands_registration_with_callbacks.py.
  • The main change is removed before callback wrapper. It was used to invoke commands registration as soon as possible but IMO it's not needed to do it as soon as possible and we can invoke registration from commands_registration_callback after processing all eager CLI options (what we did anyway but previously only as a fallback, which wasn't needed).
• Adjusted tests.