[Apollo] Tighten namespace around metrics

This tightens the namespace which are part of our Datadog Marketplace integration to just the set of operations which from the integration rather than those that are emitted by our on-prem product, Apollo Router — which emits its metrics into an `apollo.router.` prefixed namespace, which should _not_ prevent users from losing control over the management of tags in their UI.

Relates to DataDog#2529

apollo/manifest.json

@@ -33,10 +33,9 @@
         "creates_events": false
       },
       "metrics": {
-        "prefix": "apollo.",
+        "prefix": "apollo.operations.",
         "check": [
-          "apollo.operations.count",
-          "apollo.engine.operations.count"
+          "apollo.operations.count"
         ],
         "metadata_path": "metadata.csv"
       },
@@ -47,4 +46,4 @@
       "auto_install": true
     }
   }
-}
+}