Extend online view of HTML artifacts to private projects

Description

Issue #34102 (closed) allows to view HTML artifacts in a browser window instead of download them locally, but it is limited to public projects only.

Since most users need this also for private projects, a proper support to that is the scope of this issue.

Proposal

Extend online view of HTML artifacts to private projects, providing proper authentication to rescrict artifacts access.

Links / references

Master meta issue: Improvements for Java language in CI (#33943 (moved))
Online view of HTML artifacts for public projects (#34102 (closed))

Documentation blurb

Use cases

Using GitLab to create test/coverage reports in HTML format, that must be accessible only by authorized users.

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.

• Feature assurance
• Documentation
• Added to features.yml

/label ~"feature proposal"