Convert i18n link check into a manual links report

What does this MR do?

Repeats the change from gitlab!240036 (merged) in GitLab Runner.

The docs:lint i18n markdown job calls scripts/lint-i18n-docs, which runs vale, markdownlint, and lychee together. The lychee check reports "File not found" errors over docs-locale/. As the localization team builds translations incrementally, many crosslinks point to pages not yet translated, so the lychee check will likely never run green.

This MR splits the link check out of scripts/lint-i18n-docs into a separate manual report job:

• Removes the lychee section from scripts/lint-i18n-docs so the docs:lint i18n markdown job only lints prose and Markdown.
• Adds a new docs:report i18n links job that is when: manual and saves lychee output as an artifact (kept 2 weeks) for review when needed.

Related

• Related to Convert docs-i18n-lint links into an always-gre... (gitlab!240036 - merged)
• Related to Discuss: should `docs-i18n-lint links` be disab... (gitlab#602393)
• Related to Convert docs-i18n-lint links into a manual i18n... (omnibus-gitlab!9572 - merged)