Make DatePicker testable

[guykoh]

Currently DatePicker component is not intractable in tests without having access to the DatePicker component. These are the features missing in DatePicker in order to make it testable:

1. Pass props through, i.e set data-testid to the DatePicker component
2. Add ability to fill in a date value to the component - something like

await helper.page.getByTestId('datepicker-input').fill(date)