Add workers.celery.command & workers.kubernetes.command

[Miretpl]

related: #28880

This PR introduces two new fields: workers.celery.command and workers.kubernetes.command. Field workers.command is not deprecated as it was used by two worker types. Now it will be possible to use dedicated commands for both Celery and Kubernetes workers.

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[Miretpl]

There are some changes in test_workers.py regarding the workers.args command. Previously, there was only one test case for both workers.command and workers.args, and I separated them.