Reduce /read requests during call

[SystemKeeper]

The Web utilizes the dedicated /read endpoint to mark the chat as read (https://github.com/nextcloud/spreed/blob/main/docs/chat.md#mark-chat-as-read). To reduce the number of queries to the server during a call, the idea is to not use the dedicated read marker endpoint, but set the setReadMarker parameter on the long polling request instead: https://github.com/nextcloud/spreed/blob/main/docs/chat.md#chat-api

Question raised by @nickvergessen: Would that interfere with the "You have unread messages in the chat" message, when the chat is hidden in a call?

spreed/lib/Controller/ChatController.php

Lines 493 to 496 in 00a8e4a

	if ($lookIntoFuture && $setReadMarker === 1 &&
	$lastKnownMessageId > $attendee->getLastReadMessage()) {
	$this->participantService->updateLastReadMessage($this->participant, $lastKnownMessageId);
	}