Allow assigning dedicated resource managers without creating separate "virtual" users

[matt-ek]

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

Is your feature request related to a problem? Please describe.
Currently, managing resources in Nextcloud Calendar often requires creating virtual Nextcloud users to act as resource owners.

Example workflow today:

• For each resource (e.g. "parish hall", "bus", "projector"), a new Nextcloud user must be created (raum-saal, auto-bus, beamer01).
• The resource is then linked to this user.
• Resource calendars can be shared from this user account to actual responsible persons (e.g. staff, administrators).
• This way, certain people can see details, approve bookings, or manage conflicts.

While this workaround technically works, it comes with several disadvantages:

• Administrative overhead: Each resource requires a full user account (password, lifecycle, quota, policies). In larger installations (schools, NGOs, municipalities) this quickly becomes unmanageable.
• Unintuitive setup: End users and even administrators need to understand the “virtual user” concept, which is confusing and not transparent.
• Scalability issues: Managing dozens of additional user accounts solely for resource management is not a sustainable long-term approach.
• Auditability: Permissions and responsibilities are harder to trace when managed indirectly via user accounts.

Describe the solution you'd like

A native concept of "resource managers" in the Resource Management app:

• Each resource should allow assigning one or more managers directly.
• Managers have elevated permissions for that specific resource, e.g.:

1. View all details of bookings.
2. Approve or reject booking requests (if approval workflows are enabled).
3. Modify or delete bookings.

• Other users (who can book the resource) should only see the configured level of detail (busy/free, anonymized, etc.).
• This would eliminate the need for the "virtual user" workaround and make the resource management experience more intuitive and transparent.

Describe alternatives you've considered

• Virtual users (current workaround): As described, functional but complex, error-prone, and not scalable.
• Manual calendar sharing: Possible, but lacks dedicated semantics for "resource managers" and requires administrators to handle permissions on multiple layers.
• External resource booking tools: Some organizations resort to using separate tools (e.g. Room booking systems), but this breaks integration with Nextcloud Calendar.

Additional context

• In community or parish settings, resources such as parish halls, cars, or equipment often require one or more responsible persons. These persons should be able to manage and supervise bookings without the need for full admin rights.
• In schools or NGOs, the current "virtual user" method is confusing for non-technical staff, while a clear "resource managers" option would be easy to explain and use.
• A dedicated permission model would also allow for future features like delegation, approval workflows, or audit logs tied directly to resource management.

[st3iny]

Thanks for the request and the detailed write-up. I agree that having room/resource managers makes a lot of sense.

A first step would perhaps be to expose the calendars via CalDAV and then share them on a read-write basis with another managing Nextcloud user: #194