Stackdriver: Rename Stackdriver to Google Cloud Monitoring (#25807)

* Update backend

* Update frontend

* Keep old plugin id

* Update docs

* Place doc images to a new directory

* Legacy support for stackdriver-auto alignment

* Consistent plugin name

* Apply suggestions from code review

Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>
Co-authored-by: Tobias Skarhed <1438972+tskarhed@users.noreply.github.com>

* Update docs

* Update public/app/plugins/datasource/cloud-monitoring/README.md

Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>

* Add reference to the data source formerly being named Stackdriver

* Update pkg/models/datasource.go

Co-authored-by: Carl Bergquist <carl@grafana.com>

* Fix gofmt

Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>
Co-authored-by: Tobias Skarhed <1438972+tskarhed@users.noreply.github.com>
Co-authored-by: Carl Bergquist <carl@grafana.com>

packages/grafana-data/src/types/data.ts

@@ -43,7 +43,7 @@ export interface QueryResultMeta {
    * Legacy data source specific, should be moved to custom
    * */
   gmdMeta?: any[]; // used by cloudwatch
-  alignmentPeriod?: string; // used by stackdriver
+  alignmentPeriod?: string; // used by cloud monitoring
   searchWords?: string[]; // used by log models and loki
   limit?: number; // used by log models and loki
   json?: boolean; // used to keep track of old json doc values