chore: set datepicker default view to minimum date

[tshuli]

Problem

Closes #377

Solution

• set dateOptions.initDate = dateOptions.minDate

Tests

Tested on GSIB-IE

• Create date field. Set custom date range with minimum date in the distant past (e.g. 2015). Open the form in public view. Check that the datepicker opens to the month of the minimum date by default.
• Create date field with no date validation. Open in public view. Check that the datepicker opens to the current month by default.

[mantariksh]

my spidey sense is tingling because of how harmless this looks, pls test thoroughly!

[liangyuanruo]

Do consider code clarity to other developers as well - I think it can be more obvious that initDate is only set when minDate is present.