Adding a history of actions by user in the private billing section

On the top left section of the private billing section (when in a new bill), the only history we can see when actioning something related to a bill, is the "invalidating" information (we see the invalidating information in red - who invalidated it and when, as well as who created the bill).

Some of our clients have asked to see traces of who modifies a bill that was "saved": on an accounting perspective but also coming from some admins, the clinic would need to know and see if another user modifies a bill that is still open.

Otherwise, on a security perspective, anyone could go and change the status of a bill that is not closed or even cancel it, even if the clinic would have physically received the money.