website/docs: new upgrade page (#10742)

* first draft

* add to sidebar

* made mdx

* diff image add troubleshoting

* Optimised images with calibre/image-actions

* tweaks

* edits from review

* more review edits, tweaks

* tab fights

* still fighting tabs

* add link from Rel Note template

* more syntax fights

* i give up

* git hates me

* no comment

* formatting

* styling stuff

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

* merge conflict

* add Jens' edits

* fighting my rebase

* tweak

* added note on Rel Note template about versions must match

* git hates me even more today than yesterday

* tweak

---------

Signed-off-by: Jens Langhammer <jens@goauthentik.io>
Co-authored-by: Tana M Berry <tana@goauthentik.com>
Co-authored-by: authentik-automation[bot] <135050075+authentik-automation[bot]@users.noreply.github.com>
Co-authored-by: Jens Langhammer <jens@goauthentik.io>

website/docs/releases/_template.md

@@ -15,9 +15,13 @@ To try out the release candidate, replace your Docker image tag with the latest
 
 ## Upgrading
 
-This release does not introduce any new requirements.
+This release does not introduce any new requirements. You can follow the upgrade instructions below; for more detailed information about upgrading authentik, refer to our [Upgrade documentation](../installation/upgrade.mdx).
 
-### docker-compose
+:::warning
+When you upgrade, be aware that the version of the authentik instance and of any outposts must be the same. We recommended that you always upgrade any outposts at the same time you upgrade your authentik instance.
+:::
+
+### Docker Compose
 
 To upgrade, download the new docker-compose file and update the Docker stack with the new version, using these commands: