Auth: Azure AD OAuth (#20030)

* Implement Azure AD oauth

* Use go-jose and cleanup

* Update go-jose in go.mod

* cleanup

* Add unit tests

* Fix scopes

* Add documentation page

* Improve documentation

* Convert extract_role into function.

* Do not use upn and replace unique_name with preferred_username

* Configure login button

* Use official microsoft icon and color from branding guideline.

* Add Azure AD config section in sample.ini.

public/sass/_variables.generated.scss

@@ -222,6 +222,11 @@ $external-services: (
     borderColor: #b83e31,
     icon: '',
   ),
+  azuread: (
+    bgColor: #2f2f2f,
+    borderColor: #2f2f2f,
+    icon: '',
+  ),
   grafanacom: (
     bgColor: #262628,
     borderColor: #393939,