feat: add disabledDates and enabledDates to DatePicker and DateInput

[JinIgarashi]

It would be nice if particular dates can be disabled or enabled while currently only can restrict by using min and max dates.

I added following two props.

• disabledDates: Date[]. Disable dates in the array.
• enabledDates: Date[]. Enable only dates in the array. If it is used, disabledDates is ignored.
• updated documentation for these two props

Please let me know your thought on this PR.

Screenshots

• for DateInput

• for DatePicker. I added new datepicker for enabledDates.
  

• If enabledDates is used, disable year and month on dropdown

[probablykasper]

Would you agree that it makes more sense to have a property like this?

isDateDisabled: (date: Date) => boolean | undefined

[JinIgarashi]

@probablykasper Thank you for your comment. I am very sorry I was not aware there was already closed issue. IsDateDisabled can be a better idea than adding new two properties of this PR. I will try to add a callback function (probably I will create another PR for isDateDisabled).

I just let you know that I published this PR's changes to our NPM since we need this feature for our development. I will switch from ours to yours when it will have the feature to disable particular dates.
https://www.npmjs.com/package/@undp-data/date-picker-svelte

[probablykasper]

All good! In that case I'll close this PR, but I appreciate your work