feat(holiday): solar term

[curbengh]

What is it?

• Bugfix
• Feature
• Codebase improvement

Description of the changes in your PR

• Add solar term to holiday list.
• Exported from apple calendar which includes solar term when showing china holidays.
• It's a list of astronomical events, not public holiday, so a bit of novelty.
• I set all events as recurring, even though some dates may change every year. The dates are correct until 2025/11/22, if apple is correct until then. I'm assuming importing newer version of solarterm.ics will replace previously imported events with the same UID.
• Traditional chinese characters are used as they are similar enough (though not exactly the same) to japanese kanji and korean hanja, at least until the holiday feature support internationalization.

Acknowledgement

• I read the contribution guidelines.

[naveensingh]

Exported from apple calendar which includes solar term when showing china holidays.

Was it a separate option or just included with the holidays?

I'm asking because of this:

It's a list of astronomical events, not public holiday