[ja] Translate content/en/docs/reference/glossary/quantity.md into Japanese

_**Note that this issue is for Japanese Speaker**_

**This is a Feature Request**

**What would you like to be added**

Translate `content/en/docs/reference/glossary/quantity.md` into Japanese

**Why is this needed**

There is no Japanese translation for this page.
This term is referenced by 1 Japanese page via `glossary_tooltip`, so that page currently falls back to the English tooltip.

**Comments**

- File to translate:
- https://github.com/kubernetes/website/blob/main/content/en/docs/reference/glossary/quantity.md
- Related page:
- https://kubernetes.io/ja/docs/reference/glossary/?all=true#term-quantity
- Reference (an already translated glossary term):
- https://github.com/kubernetes/website/blob/main/content/ja/docs/reference/glossary/limitrange.md

日本語に翻訳する際は、以下のドキュメントを参考にしてください。

- Japanese Localization document: https://kubernetes.io/ja/docs/contribute/localization/