website/docs: prepare 2023.3 release notes (#4889)

* website/docs: prepare 2023.3 release notes

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

* Apply suggestions from code review

Co-authored-by: Tana M Berry <tanamarieberry@yahoo.com>
Signed-off-by: Jens L. <jens@beryju.org>

* add better docs for custom css

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

---------

Signed-off-by: Jens Langhammer <jens@goauthentik.io>
Signed-off-by: Jens L. <jens@beryju.org>
Co-authored-by: Tana M Berry <tanamarieberry@yahoo.com>

website/docs/interfaces/admin/customization.mdx

@@ -7,3 +7,7 @@ How many items should be retrieved per page. Defaults to 20.
 ### `settings.theme.base`
 
 Configure the base color scheme. Defaults to `automatic`, which switches between dark and light mode based on the users' browsers' preference. Choices: `automatic`, `dark`, `light`.
+
+import Global from "../_global/global.mdx";
+
+<Global />