Add end-to-end test to delete board via the graphical user interface

What does this MR do?

This MR is a continuation of !18474 (merged), and it closes gitlab-org/quality/testcases#226 (closed) by implementing the second scenario described on it.

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