introduce `fetchUnreadNotifs` fetcher in `notifications-fetcher`. We want to extract this logic so that we can use this in other situations for example, when we want to rescind a reaction message
[[ https://linear.app/comm/issue/ENG-2644#comment-f27983a1 | More context ]]
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Linear Task: [[ https://linear.app/comm/issue/ENG-2644/rescind-a-reaction-message-notif-with-a-remove-action-from-the | ENG-2644 ]]