Fixes#16896
The problem was that we relied on the `SIGNAL_PINNED_MESSAGES_LOADED` event to apply the pinned status to messages, but that only happens at the start and a lot of messages are not loaded at start if they are not in the first 30 messages.
To fix this, I just added `pinnedBy` to the Message object in status-go. This way, we can easily tell straight from the MessageDto if a message is pinned and by whom.
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