[RFC]: support of new Talk features in Desktop with old servers

[Antreesy]

Features a-like this one (pure frontend, server is only needed for cross-device support) e.g.:

• call without media https://github.com/nextcloud/spreed/issues/13446
• blur background https://github.com/nextcloud/spreed/pull/13490
• compact conversations list https://github.com/nextcloud/spreed/issues/11697

can be supported with Desktop client with old servers, but keep it in BrowserStorage instead of sending a request to backend

Originally posted by @Antreesy in #957

[nickvergessen]

This is not completed? Or did you patch anything here or in spreed?

[ShGKme]

Background

Frontend checks for supported features via capabilities. Capabilities are defined by server. But sometimes server capability is actually only about the user settings (config). So the feature can work fine on local-level settings.

Proposal

For such capabilities only use the capability for config setting on the server and use browser storage as a fallback.