Out of office: expose setting endpoint via OCS

[ChristophWurst]

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Is your feature request related to a problem? Please describe.

As a Nextcloud client developer I want to integrate with #40616. The APIs added are only usable for the web app.

Describe the solution you'd like

Expose the APIs as OCS instead. This makes them consumable by clients.

Describe alternatives you've considered

N/a

Additional context

Suggested by @nickvergessen in #40767 (comment)