Add the translation of Japanese

[kohju]

Description

Just a Japanese translation for Japanese users.
These days, some part of VMware users are looking for an alternative virtual environment instead of VMware.
It seems like an opportunity to raise XenOrchestra awareness for Japanese Users.

This translation is not perfect now, but I will continue to translate if I have time.

Checklist

• Commit
  • Add the pulldown option "ja", so users can select Japanese in index.js.
  • Add the ja.js in intl.

[olivierlambert]

Hello @kohju and thank you very much for your contribution. I'll ping the team so we'll be sure to review it before our next release 👍

[pdonias]

@kohju Thanks for the PR! We just need to update the changelog and it's ready to merge :) I would do it but I don't have permissions to push to your branch. In the file CHANGELOG.unreleased.md, could you add:

• This line at the end of the Enhancements section:

- [i18n] Japanese translation (PR [#7582](https://github.com/vatesfr/xen-orchestra/pull/7582))

• And this at the end of the package list at the bottom of the file:

- xo-web minor

Thanks!

[kohju]

@pdonias
Thank you for your edition instead of me.

I have a question.
I want to update Japanese translation script, what should I do?

1. create new branch or merge edge master to this branch?
2. pull request same way and add package list 'xo-web minor' and other to do?

Regards,
TAKI.

[pdonias]

1. You can create a new branch from the up-to-date master branch, it will be easier to follow the git history
2. Ideally, you would add a changelog entry in "Enhancements" like - [i18n] Update Japanese translation (PR [#xxxx](https://github.com/vatesfr/xen-orchestra/pull/xxxx)) and then - xo-web minor in "Packages to release". However, if you don't want to worry about the changelog, you can simply allow us to push to your branch and we'll do that for you right before merging your PR! :)

Thanks again for you contribution!

And actually, I forgot to close this PR in favor of #7605