Ability to push custom commands to Matomo

At the moment only django-analytical allows [custom variables](https://django-analytical.readthedocs.io/en/latest/services/matomo.html#user-variables) to be passed into Matomo.

It would be nice, if we can pass custom commands similar way, so features like [track 404](https://matomo.org/faq/how-to/faq_60/) can be achieved easily.