Added a downward chevron sprite icon to environments dropdown in Ultimate

What does this MR do?

This MR for issue #11562 (closed) makes a downward chevron sprite icon visible next to the dropdown button for the various dashboards in the app header.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Style guides

Performance and testing

• Tested in all supported browsers

Closes #11562 (closed)