Get a list of messages that match the search conditions
If you search a specific conversation, messageList will contain all matching messages in that conversation.
If you search all conversations, either of the following two cases will apply:
- If there is more than one matching message in a conversation, messageList will be empty. You can display a message like "messageCount results found" on the UI.
- If there is only one matching message in a conversation, messageList will contain that message. You can display the message on the UI with the matching keywords highlighted.