Add E2E test of pipelines for merged results

What does this MR do?

Adds an E2E test of pipelines for merged results

• Adds QA selectors.
• Changes the code for expanding merge request settings to be consistent with other similar code. And Updates the rebase merge request test that used the old code.

Closes gitlab-org/quality/testcases#203 (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