CloudMonitoring: Use response unit instead of metric descriptor unit (#32928)

* improve unit detection

* Update docs/sources/datasources/google-cloud-monitoring/_index.md

Co-authored-by: Ursula Kallio <73951760+osg-grafana@users.noreply.github.com>

* goimports

* fix typo

* golint fixes

* Update docs/sources/datasources/google-cloud-monitoring/_index.md

Co-authored-by: Diana Payton <52059945+oddlittlebird@users.noreply.github.com>

* Update docs/sources/datasources/google-cloud-monitoring/_index.md

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

* Update docs/sources/datasources/google-cloud-monitoring/_index.md

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

* Update docs/sources/datasources/google-cloud-monitoring/_index.md

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

* Update docs/sources/datasources/google-cloud-monitoring/_index.md

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

* pr feedback

* Update docs/sources/datasources/google-cloud-monitoring/_index.md

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

Co-authored-by: Ursula Kallio <73951760+osg-grafana@users.noreply.github.com>
Co-authored-by: Diana Payton <52059945+oddlittlebird@users.noreply.github.com>
Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

pkg/tsdb/cloudmonitoring/test-data/1-series-response-agg-one-metric.json

@@ -42,5 +42,6 @@
         }
       ]
     }
-  ]
+  ],
+  "unit": "By/s"
 }

pkg/tsdb/cloudmonitoring/test-data/2-series-response-no-agg.json

@@ -141,5 +141,6 @@
         }
       ]
     }
-  ]
+  ],
+  "unit": "10^2.%"
 }