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/sidebars.js

@@ -21,6 +21,7 @@ const docsSidebar = {
             items: [
                 "installation/docker-compose",
                 "installation/kubernetes",
+                "installation/upgrade",
                 "installation/beta",
                 "installation/configuration",
                 "installation/reverse-proxy",