Integrate logs query hints with UI

• Fetch Logs search metadata (maybe with mocked data if API not available yet ) gitlab-org/gitlab!152144 (merged)
• Add suggestions for service_names and trace_flags, severity_names etc ( gitlab-org/gitlab!151993 (merged))
• On Logs table, do not show severity_text, but instead have an hardcoded mapping of number to name ( gitlab-org/gitlab!151990 (merged))
• Remove mocks when API ready gitlab-org/gitlab!152502 (merged)
• Pass metadata to filtered search gitlab-org/gitlab!152358 (merged)
• Make logs API calls cancellable gitlab-org/gitlab!152194 (merged)