Rewrite the 'celery' command to use Click

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This is part of a series of PRs breaking up #22613 into smaller, more reviewable chunks. The end result will be rewriting the existing airflow CLI to use Click instead of argparse. For motivation, please see #22708.

This PR adds the celery subcommand to the airflow-ng command. It's exactly the same as the airflow celery command, it's just implemented with Click. This PR also includes an additional, separate test file for the Click celery subcommand. The intent there is to simply remove the test files for the old commands once the Click-based airflow-ng command supersedes and replaces the argparse-based airflow command.

For comparison to the modules this supersedes:

• airflow/cli/commands/celery_command.py
• tests/cli/commands/test_celery_command.py

Original author: @hankehly astronomer#1495

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@hankehly Can I get your 👍 on this?

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From this discussion, there is more groundwork and research necessary before we can evaluate rewriting the CLI with Click.