Added "curated dashboards" information and broke down, rearranged topics. (#30659)

* Change to introduction section.

* Checkin changes.

* Check in changes.

* Updated heading levels for better readability.

* Checkin changes.

* Broke down topic and fixed relrefs. Also, resized images.

* Added one more relref from preconfig dashboards to main topic.

* Adding Eric's changes.

* Added alias.

* Updated alias with correct syntax, also updated description typo for "Preconfigured dashboards"s

* Checking in changes from Diana.

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

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

* One last change.

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

docs/sources/datasources/_index.md

@@ -19,7 +19,7 @@ The following data sources are officially supported:
 - [AWS CloudWatch]({{< relref "cloudwatch.md" >}})
 - [Azure Monitor]({{< relref "azuremonitor.md" >}})
 - [Elasticsearch]({{< relref "elasticsearch.md" >}})
-- [Google Cloud Monitoring]({{< relref "cloudmonitoring.md" >}})
+- [Google Cloud Monitoring]({{< relref "google-cloud-monitoring/_index.md" >}})
 - [Graphite]({{< relref "graphite.md" >}})
 - [InfluxDB]({{< relref "influxdb.md" >}})
 - [Loki]({{< relref "loki.md" >}})