Convert docs-i18n-lint links into a manual i18n links report

What does this MR do?

Repeats the change from gitlab!240036 (merged) in omnibus-gitlab.

The docs-i18n-lint links job runs lychee over doc-locale/ and reports "File not found" errors. As the localization team builds translations incrementally, many crosslinks point to pages not yet translated, so the job will likely never run green. It was only kept passing via allow_failure: true.

Instead of a lint job that fails, this converts it into a manual report job:

• Renamed docs-i18n-lint links -> docs-i18n-report links.
• Changed to when: manual and drops allow_failure, since it's no longer a required pipeline check.
• The lychee output is piped to docs-i18n-links-report.txt and saved as an artifact (kept 2 weeks) so it can be reviewed 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)
• Resolves docs-i18n-lint links job fails (#9992 - closed)