Make possibility to hook into the query of the metrics aggregate methods

[maul75]

In my use case I need metrics on a user basis, but there is no way to pass anything to the aggregate function of the metrics classes. I'm currently extending the respective classes myself and overwriting the aggregate function. But perhaps it would simply be solvable to offer an opportunity to hand something over here.

Example of what I added to my custom aggregate in the Laravel\Nova\Metrics\Value class:

$userCustomers = $request->user()->customers()->get()->pluck('id')->toArray(); $query->whereIn('customer_id', $userCustomers);

In addition, the getDefaultTimezone method should not be set private to use it also in extended classes.