Core and modules scheduled update

[DavidePrincipi]

When a Subscription is activated, enable automatic and managed updates for:

• [x] core
• [x] modules
• [x] OS (Rocky)

Automatic update can be manually enabled without Subscription too, but default repositories are not managed by Nethesis support.

Tasks

• [x] CNAME subscription.nethserver.com
• [x] Serve repodata.json from Porthos (u4)
• [x] Implement scheduled updates for core, modules and base OS (Rocky Linux only)
• [x] Update admin's manual with scheduled updates information

Discussion https://mattermost.nethesis.it/nethesis/pl/tejsohr9ejdg5r18pnfqiurdfw

[DavidePrincipi]

Testing release https://github.com/NethServer/ns8-core/releases/tag/2.5.0-dev.3

[DavidePrincipi]

Released with core 2.5.0