Create Japanese documentation directory

What does this MR do and why?

Adding Japanese Documentation Structure

This MR adds a Japanese translated documentation file within a new /docs-locale/ja-jp/ directory structure, which will enable http://docs.gitlab.com/ja-jp/. We're starting with a single translated file to establish the directory structure, with more translations to follow.

Closes Create /doc-locale/ja-jp directory in upstream ... (gitlab-com/localization/docs-site-localization#121 - closed)

Related Changes

This Runner MR has sister counterparts across GitLab projects that comprise our documentation site (GitLab, Operator, Charts, & Runner). A change to the docs site will follow to launch docs.gitlab.com/ja-jp/ that will use content from the /doc-locale/ja-jp/ directory.

Please see the SSOT issue for all information related to creating the /doc-locale/ directory structure to launch the Japanese documentation site.

Specific Changes of this MR

1. Adds a single Japanese translated file to /doc-locale/ja-jp/
2. Updates CODEOWNERS to designate @gitlab-com/localization/maintainers as owners of the new /doc-locale directory
3. Creates i18n-specific CI jobs that mirror existing doc CI to lint content: docs:lint i18n markdown
4. Create rules in the .gitlab/ci/_rules.gitlab-ci.yml for .docs-i18n-patterns
5. Create script scripts/lint-i18n-docs - currently this is duplicating scripts/lint-docs with changes to the correct path
6. And related changes to the MAKEFILE

References

1. https://gitlab.com/gitlab-com/localization/docs-site-localization/-/issues/102 -> Primary issue with all context related to this work.
2. gitlab-com/localization&104 (closed) -> primary epic with more context for all the relevant issues
3. gitlab-com/localization/docs-site-localization#121 (closed) -> Engineering issue for this MR.

How to set up and validate locally

docs:lint i18n markdown: Test markdown linting for localized content

1. Make edits to /docs-locale/ja-jp/register/_index.md that will fail the markdown linter.
   • For example: remove spaces around lists, use inconsistent heading styles, or add improper indentation
2. Run the linter locally to verify it catches the issues for the /docs-locale directory
   • markdownlint-cli2 'docs-locale/**/*.md'
3. Run Vale locally to see the validation errors:
   • make lint-i18n-docs VALE_MIN_ALERT_LEVEL=error
   • vale --config ".vale.ini" "docs-locale/ja-jp/register/_index.md"

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