Add E2E test of NPM registry

What does this MR do?

Adds an E2E test of the NPM registry

• Adds a docker service to publish an NPM package
• Adds QA selectors and page objects for the packages UI
• Adds Runtime::Fixtures.with_fixtures which allows fixtures to be created on-the-fly

Requires a new gitlab-qa scenario to enable the packages feature in omnibus: gitlab-qa!293 (merged)

Closes gitlab-org/quality/testcases#220 (closed)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content