Convert docs-i18n-lint links into an always-green i18n links report

What does this MR do?

Implements the suggestion from Marcel in #602393 (note).

The docs-i18n-lint links job runs lychee over doc-locale/ and reports thousands of "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 test that fails, this converts it into a report job:

• Renamed docs-i18n-lint links → docs-i18n-report links.
• Always runs green: lychee output is piped to a report artifact and the job exits successfully (|| true), so allow_failure is no longer needed.
• The lychee output is saved as docs-i18n-links-report.txt artifact (kept 2 weeks) so it can be reviewed when needed.

Related

• #602393