feat: add japanese language support

[ikrammt]

This pull request introduces support for the Japanese language (ja) #2581 in the react-big-calendar library. This enhancement expands the user base by enabling users who prefer Japanese to interact with the calendar interface and labels in their native language.

[cutterbl]

I appreciate your general thought process here. But, Big Calendar, on it's own, does not provide any speciific language localization support, but rather the tools and props necessary to allow a developer to localize as necessary. While you've improved this story a bit, showing how to do this in Japanese, perhaps a better option may be in providing a more in depth story in the 'Guides' section, detailing the ins and outs of properly providing localization support.

[ikrammt]

Thanks for the feedback! You're absolutely right, Big Calendar itself doesn't handle localization directly. However, showcasing a basic example like the Japanese one is a good start.I will definitely add it to the 'Guides' section.