test: remove hard-coded metric count

Prior to this commit, adding any metric to the catalog (and only the
catalog) would cause the end_to_end_ng_cases::metrics::test_metrics test
to fail due to asserting an exact number of metrics observed.

This commit changes the check condition to a more permisive >= rather
than ==.

influxdb_iox/tests/end_to_end_ng_cases/metrics.rs

@@ -16,13 +16,13 @@ pub async fn test_metrics() {
             Step::WriteLineProtocol(lp),
             Step::WaitForReadable,
             Step::VerifiedMetrics(Box::new(|_state, metrics| {
-                assert_eq!(
+                assert!(
                     metrics
                         .trim()
                         .split('\n')
                         .filter(|x| x.starts_with("catalog_op_duration_ms_bucket"))
-                        .count(),
-                    180
+                        .count()
+                        >= 180
                 );
             })),
         ],