Add Japanese translation of "Legacy Selenium 1"

[kzhirata]

Description

Translating document "Legacy Selenium 1" from English to Japanese

• legacy_docs/_index.ja.md
• legacy_docs/selenium_rc.ja.md

Motivation and Context

Types of changes

• Change to the site (I am attaching a screenshot showing the before and after)
• Code example added (and I also added the example to all translated languages)
• Improved translation
• Added new translation (and I also added a notice to each document missing translation)

Checklist

• I have read the contributing document.
• I have used hugo to render the site/docs locally and I am sure it works.

[diemol]

Thank you @kzhirata!