Follow-up from "Create Japanese documentation directory"

The following discussion from !4220 (merged) should be addressed:

• @rasamhossain started a discussion: (+2 comments)

  Hi there @marcel.amirault,

  Thank you so much for looking into the Runner MR earlier. Hoping to get your attention on this Charts MR as well. Would highly appreciate if you could take a moment to review this.

What does this Issue do and why?

Adding validation for Japanese Documentation

The previous MR added a Japanese translated documentation file within a new /doc-locale/ja-jp/ directory structure, which enables http://docs.gitlab.com/ja-jp/.

Scope of this issue

In the parent MR, we already added the following:

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

To validate the translated files in the parent MR, we need to create i18n/Localization pipelines, markdown lints for the verification purpose. The goal of this particular issue is to tackle the following

1. Creates a new DOCS_LOCALIZATION_PIPELINE rule that is triggered when a branch name is prepended with docs-i18n
2. Creates i18n-specific CI jobs that mirror existing doc CI to lint content:
   • docs-lint-i18n content
   • docs-lint-i18n markdown

Important Notes

1. The docs Hugo project is not currently configured to consume content from the /doc-locale/ directory. When it is, we will iterate on the DOCS_LOCALIZATION_PIPELINE to build the docs in the same way the DOCS_PIPELINE does.
2. We are simply verifying the file is properly linted

Related Changes

This Charts 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.

References

1. Link to the Parent MR: Create Japanese documentation directory (!4220 - merged)
2. https://gitlab.com/gitlab-com/localization/docs-site-localization/-/issues/102 -> Primary issue with all context related to this work.
3. gitlab-com/localization&104 (closed) -> primary epic with more context for all the relevant issues
4. https://gitlab.com/gitlab-com/localization/docs-site-localization/-/issues/119 -> Engineering issue for the Parent MR.