Include userCacheBuster in talkHash

[SystemKeeper]

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Is your feature request related to a problem? Please describe.
Currently we only include the system cache buster value when we create our talk hash:

spreed/lib/Controller/RoomController.php

Line 157 in be60841

$this->config->getAppValue('theming', 'cachebuster', '1')

Describe the solution you'd like

When a user changes the theming settings, the hash does not get invalidated. Therefore clients might not refetch the server capabilities and update the theming. We might think about including the user cache buster as well:

https://github.com/nextcloud/server/blob/eaa6d96cf7d447c5b9db5fcb0657dad5bb9c88af/apps/theming/lib/Util.php#L339-L340