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/fundamentals/_index.md

@@ -0,0 +1,13 @@
++++
+title = "Alerting fundamentals"
+weight = 110
+aliases = ["/docs/grafana/latest/alerting/metrics/", "/docs/grafana/latest/alerting/unified-alerting/fundamentals/"]
++++
+
+# Alerting fundamentals
+
+This section covers the fundamental concepts of Grafana 8 alerting.
+
+- [Alertmanager]({{< relref "./alertmanager.md" >}})
+- [State and health of alerting rules]({{< relref "./state-and-health.md" >}})
+- [Evaluating Grafana managed alerts]({{< relref "./evaluate-grafana-alerts.md" >}})