Docs: Refactor alerting documentation (part 1) (#48664)

* Initial commit

* Moved files, ad fixed broken relrefs.

* Fixed other broken relrefs

* More changes.

* Fixing broken relrefs

* More changes.

* Fixed last of the broken links

* More re-org.

* Added aliases and some weight adjustments

* More aliases.

* Fix fundamentals topic.

* Fixed remaining metadata issues

* Ran prettier

docs/sources/alerting/alert-groups.md

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+title = "Alert groups"
+description = "Alert groups"
+keywords = ["grafana", "alerting", "alerts", "groups"]
+weight = 400
+aliases = ["/docs/grafana/latest/alerting/unified-alerting/alert-groups/"]
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+
+# Alert groups
+
+Alert groups show grouped alerts from an Alertmanager instance. By default, the alerts are grouped by the label keys for the root policy in [notification policies]({{< relref "./notifications/_index.md" >}}). Grouping common alerts into a single alert group prevents duplicate alerts from being fired.
+
+## View alert groupings
+
+1. In the Grafana menu, click the **Alerting** (bell) icon to open the Alerting page listing existing alerts.
+1. Click **Alert grouping** to open the page listing existing groups.
+1. From the **Alertmanager** drop-down, select an external Alertmanager as your data source. By default, the `Grafana` Alertmanager is selected.
+1. From **custom group by** drop-down, select a combination of labels to view a grouping other than the default. This is useful for debugging and verifying your grouping of notification policies.
+
+If an alert does not contain labels specified either in the grouping of the root policy or the custom grouping, then the alert is added to a catch all group with a header of `No grouping`.
+
+## Filter alerts
+
+You can use the following filters to view alerts that match specific criteria:
+
+- **Search by label:** In **Search**, enter an existing label to view alerts matching the label. For example, `environment=production,region=~US|EU,severity!=warning`
+- **Filter alerts by state:** In **States**, select from Active, Suppressed, or Unprocessed states to view alerts matching your selected state. All other alerts are hidden.