[stable32] feat(settings): Add an app config to set the default for guests sound

[backportbot]

Backport of #16379

Warning, This backport's changes differ from the original and might be incomplete ⚠️

Todo

• Review and resolve any conflicts
• Amend HEAD commit to remove the line stating to skip CI

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[miaulalala]

public function getPlaySoundsDefaultForGuests(): bool { return $this->appConfig->getAppValueBool('guests_play_sounds', true); }

misses

public function getPlaySoundsDefaultForGuests(): bool {
	return $this->appConfig->getAppValueBool('guests_play_sounds', true);
}