Allow Users to override tracker class

[sumit4613]

Motivation

Currently Tracker is tightly coupled with TrackingModelMixin, if we want to add some methods that replicate the behavior of model_utils.FieldTracker methods, we need to override the TrackingModelMixin and rewrite the tracker property and write a new Tracker class with the required methods.

To avoid this, I'm adding a new attribute tracker_class to TrackingModelMixin which defaults to Tracker.

This helps us to easily override the Tracker and write required methods, without duplicated lines of code.

@drozdowsky @browniebroke please let me know what you think about this approach.

Finally, thank you ❤️ for creating this library, it helped me solve some problems that were coming up because of FieldTracker.

[browniebroke]

I'm not a maintainer, but as a user of this lib, I can see how this might be useful 👍🏻

I left an idea/suggestion, although it doesn't have to be implemented.

[browniebroke]

Is this doing anything? Seems like it can be removed...

[browniebroke]

I imagine it might convenient to be able to configure the same Tracker class project-wide, rather than setting this attribute on each models that subclass TrackingModelMixin.

With that in mind, I would suggest a Django setting TRACKING_MODEL_TRACKER_CLASS (or something along these lines) to set an import path for a class to use everywhere, whihc value would default to "tracking_model.Tracker".

However, it does make the implementation a bit more complicated. A keyword here is "imagine": it's not a problem I faced, just something I think I might need.

[sumit4613]

able to configure the same Tracker class project-wide

For project-wide usage, I thought that one could easily subclass TrackingModelMixin and override the tracking_class and use it everywhere. (Took DRF's approach here)

But yeah, from the end user perspective, this settings approach would completely eliminate the overriding.

[browniebroke]

That's actually a great solution, much simpler and direct than a setting.

[drozdowsky]

Hey, thanks for PR, I will look into it shortly, seems like I don't get notifications here so sorry for late response (gotta make sure it does not happen again too).
I still have to think it through if we can make it a bit more simple but I like the overall approach and seems like a good idea

[drozdowsky]

Hi @sumit4613,
Please see my 'improvements', if you have no objections I will merge it, let me know, once again thanks for contrib.!

[sumit4613]

Hey @drozdowsky, your changes look good to me. Please go ahead, no objections.