Add slot(s) for preset range elements

[rvmourik]

Describe the solution you'd like
The datepicker is very dynamic with all the available slots, imho there is one (or two) missing. There is no possibility to use a slot for the dp__preset_ranges container. If this would be made available it is possible for example to add an explanatory text above the available ranges.

In addition (I do not need it at the moment) a slot for the dp_preset_range it self would also be a welcome addition I think.

Describe alternatives you've considered
I've looked through the code for another solution, but besides adding a ::before hack which is not future proof (for example in combination with multilingual strings)

Additional context

[rvmourik]

Thanks @Jasenkoo for implementing this.