Add link checking to i18n docs linting

What does this MR do?

Adds link validation to the internationalized (i18n) documentation linting process using Lychee. This will communicate what links are broken, but not fail the job. It is a known issue that links will fail until documentation is fully translated.

Changes

1. Adds Lychee link checker to scripts/lint-i18n-docs to validate links in localized documentation
2. Renames scripts/docs_i18n_verify_paths to scripts/docs-i18n-verify-paths for consistency with naming conventions
3. Updates CI configuration comment to reflect link checking addition

Why was this MR needed?

Communicate what links in internationalized documentation are broken. Since we know these will exists until documentation is full translated, we allow it to fail.

What's the best way to test this MR?

Run make lint-i18n-docs locally with Lychee installed to verify link checking works on i18n documentation.

Related Issues and MR

• Related gitlab-com/localization/docs-site-localization#734
• Related gitlab-com/localization/docs-site-localization#333 (closed)
• gitlab-org/charts/gitlab!4633 (merged)
• gitlab!212317 (merged)
• gitlab-org/cloud-native/gitlab-operator!1319 (merged)
• omnibus-gitlab!8869