Make DatePicker testable

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)
```