Docs: What's new, Upgrade guide, and breaking changes v12.0 (#102748)

Co-authored-by: Jacob Valdez <jacob.valdez@grafana.com>
Co-authored-by: Timur Olzhabayev <timur.olzhabayev@grafana.com>

docs/sources/shared/upgrade/intro_2.md

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+---
+headless: true
+labels:
+  products:
+    - enterprise
+    - oss
+title: Upgrade guide introduction
+---
+
+We recommend that you upgrade Grafana often to stay current with the latest fixes and enhancements.
+Because Grafana upgrades are backward compatible, the upgrade process is straightforward, and dashboards and graphs will not change.
+
+In addition to common tasks you should complete for all versions of Grafana, there might be additional upgrade tasks to complete for a version.
+
+{{% admonition type="note" %}}
+There might be breaking changes in some releases. We outline all these changes in the [What's New](https://grafana.com/docs/grafana/<GRAFANA_VERSION>/whatsnew/) document.
+{{% /admonition %}}
+
+For versions of Grafana prior to v9.2, we published additional information in the [Release Notes](https://grafana.com/docs/grafana/<GRAFANA_VERSION>/release-notes/).
+
+When available, we list all changes with links to pull requests or issues in the [Changelog](https://github.com/grafana/grafana/blob/main/CHANGELOG.md).
+
+{{% admonition type="note" %}}
+When possible, we recommend that you test the Grafana upgrade process in a test or development environment.
+{{% /admonition %}}