[ja] Support ja-kanji template extraction

[daxida]

Closes #1587

It doesn't parse every argument, but most of what I consider to be of value. It can always be easily tweaked in the future to be more precise but from what I could test it worked fine.

For @xxyzz , does the extraction of the template happen at the right place, or should I have put it somewhere else. I mean the changes in src/wiktextract/extractor/ja/page.py:

It usually happens at this level in Wiktionary:

=={{L|ja}}==
[[Category:{{ja}}]]
{{ja-kanji|常用=イン|呉音=ウン|漢音=ウン|慣用音=イン<ヰン|訓=ひびき}}

https://ja.wiktionary.org/wiki/韻#日本語

For everyone, should I have used a Form instead of Sound, since it is mostly a string and some tags? Much like transliterations are forms with the transliteration tag. I even had a KanjiReading class at some point, but it was pretty much a simpler Form.