Limit active cam users per talk room

[!TIP]

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Feature request

Which Nextcloud Version are you currently using: V34.0.1
Is your feature request related to a problem? Please describe.
Users always frustrated when the amount of active web cams in a call/room is above the limit of the underlying infrastructure resources. The more people switching their cam on the quality of the video call drops due to infrastructure limits.

Describe the solution you'd like
It would be nice, if there would be an option to set the limit of active web cam users in a call/talk room to secure a specific quality of the video call based on the underlying infrastructure capabilities.

Describe alternatives you've considered
Provide a clear and concise description of any alternative solutions or features you've considered.

Additional context
Additional/optional:

• When the limit was hit, a message should/could inform participants about that limit.
• With V34 Nextcloud Talk introduced "Conversation types" to let the user choose out of set of presets for talk calls. It would be nice if there would be an option to specify custom conversation types including the requested limit for active cam users. But this is something to be discussed in another issue...

No files, tests, or entry points are identified in the issue. First clarify the scope for configuring a per-room active webcam limit, including whether it belongs in conversation types and what participants should see when the limit is reached; done means the limit is enforced and the participant-facing behavior is defined.