Expose currentYear as part of the DayTemplateContext

[CarlosTorrecillas]

Feature request description:

Expose currentYear property as part of the DayTemplateContext:

https://ng-bootstrap.github.io/#/components/datepicker/api#DayTemplateContext

At the moment it is available the currentMonth however it would be nice if the currentYear could also be exposed. The reason for this request is that there are some custom checks performed against the date to apply certain CSS. In order to achieve that, I use current month but also the current year therefore my validation cannot be fully completed.

I thought that would be already exposed but when I added the let-currentYear="currentYear" but got undefined and confirmed in the current documentation that property is not exposed?

Versions of Angular, ng-bootstrap and Bootstrap:

Angular: 7.0.1

ng-bootstrap: 4.0.0

Bootstrap: 4.1.3