[change] Update command name to delete_old_radiusbatch_users

[praptisharma28]

Following the recent changes made in the https://github.com/openwisp/openwisp-radius/issues/496, the command name for deleting old users has been updated from delete_old_users to delete_old_radiusbatch_users for improved clarity and functionality.

As part of maintaining consistency across the OpenWISP project, it's imperative to update the command name in the docker-openwisp repository as well. This ensures coherence in naming conventions and functionality alignment

Proposed Change: Change the name of the delete_old_users command to delete_old_radiusbatch_users.

Update the documentation if required.

Similar to https://github.com/openwisp/ansible-openwisp2/issues/463 Refer https://github.com/search?q=repo%3Aopenwisp%2Fdocker-openwisp%20delete_old_users&type=code to know it's traces.

[praptisharma28]

@nemesifier have a look.

[pandafy]

Thanks for opening the issue @praptisharma28 👏🏼

[praptisharma28]

@nemesifier I am working on this one.