Add new Setting "Auto Shutdown" to list of hidden settings

[YetAnotherGerrit]

In the next release, we will add a new Setting "Auto Shutdown" that should be explained somewhere in the admin documentation.

WIP: Devs please add details about the Setting-variable here, then you can remove the issue-assignement

Tasks

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1. Add and describe new setting
2. Remove APP_RESTART_CMD (e.g. here)
3. Check also admin docs if this is mentioned and replace it (see Maintenance: Changed text about restart handling (#590 system docs) zammad-admin-documentation#734)

[mantas]

The new variable is called auto_shutdown. It's set to true by default. When it's enabled, all Zammad services will reboot automatically where RESTART_CMD was used before. E.g. when adding a custom field to objects.

When this variable is set to false, it will simply show message asking to restart manually.

Setting auto_shutdown=false would be beneficial in very rare situations only. E.g. when debugging something or using source installation without proper system services manager like systemd

@mgruner did I miss anything?

[MrGeneration]

Is RESTART_CMD no longer a thing? If it is, is it discontinued...?

[mantas]

Is RESTART_CMD no longer a thing? If it is, is it discontinued...?

Yes. Soon it will be replaced by self-restart. Processes will stop themselves and systemd will catch that to restart them.