The 'Storage Classes' link is nested under the Rook sidebar button, not
at the top level. Expand the Rook section before asserting visibility.
Also uses /rook/i case-insensitive regex and waits for the plugins list
to render before searching.
Add waitForSidebar helper function with explicit sidebar visibility wait
and networkidle state to ensure page is fully loaded before assertions.
This addresses flaky E2E tests where elements were not consistently
found due to timing issues during page transitions.
Chris Farhood