Add e2e tests to verify that the GOUI works correctly within GitLab

• Add e2e sanity tests to verify that the observability iframe loads correctly when embedded within GitLab ( either in the nav menu and inline embedding)
• Verify that navigation works correctly
• Need to decide whether we want it on GL or Observability pipeline ( or both? )
• Maybe add screenshot testing as well?
• Can be promoted to Epic and create more issues if we want to tackle adding multiple tests separately

We don't have yet the tools to run this, but it's WIP ( e.g. opstrace!1766 (merged) )