Add support for Umm al-Qura Hijri calendar

[Jawed-Poya]

Hi 👋,

First, thank you for your great work on react-multi-date-picker. It's a very useful and flexible date picker.

I’m currently working on a project that requires displaying Islamic dates based on the Umm al-Qura calendar, which is the official Hijri calendar used in Saudi Arabia. This calendar differs slightly from the astronomical Hijri calendar — often by one day — and is used in many religious and government applications.

I noticed that the current arabic calendar is based on the standard Hijri system, and doesn't match Umm al-Qura. Would it be possible to:

• Add built-in support for the Umm al-Qura calendar, OR
• Allow us to plug in a custom calendar, OR
• Provide a documented example of how to extend date-object with custom calendar logic?

If needed, I’d be happy to help with development or testing.

Thanks again!

— Jawed Poya