Move the merge request reports tab from EE to CE

What does this MR do and why?

Make the Reports tab available on all tiers. The tab partial, its pane, the reports controller action, its template and the sticky header entry all move from EE to CE.

The security_dashboard licence check is gone, so the tab now appears on every merge request. Security scan and license compliance reports stay Ultimate and keep their EE metrics. The code quality report and the three shared event definitions gain the free and premium tiers.

References

• Depends on !252599 (merged)

Screenshots or screen recordings

Before	After

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