Update doc/observability/metrics.md

Co-authored-by: Jason Madigan <[email protected]>

doc/observability/metrics.md

@@ -119,7 +119,7 @@ traffic belongs to.
 The 2nd part of the query uses the `gatewayapi_httproute_labels` metric and the
 `label_replace` function. The `gatewayapi_httproute_labels` metric gives a list
 of all httproutes, including any labels on them. The HTTPRoute in this example
-has a label called 'service', set to be the same as the istio service name.
+has a label called 'service', set to be the same as the Istio service name.
 This allows us to join the 2 results set.
 However, because the label doesn't match exactly (`destination_service_name` and `service`),
 we can replace the label so that it does match. That's what the `label_replace`