Devenv:SAML: devenv block with saml test app (#17733)

* Devenv:SAML: devenv block with saml test app

Includes documentation, couple custom users and
actual docker-compose of course :)

Ref: #4780

devenv/docker/blocks/saml/users.php

@@ -0,0 +1,21 @@
+<?php
+$config = array(
+    'admin' => array(
+        'core:AdminPassword',
+    ),
+    'grafana-userpass' => array(
+        'exampleauth:UserPass',
+        'saml-admin:grafana' => array(
+            'groups' => array('admins'),
+            'email' => 'saml-admin@grafana.com',
+        ),
+        'saml-editor:grafana' => array(
+            'groups' => array('editors'),
+            'email' => 'saml-editor@grafana.com',
+        ),
+        'saml-viewer:grafana' => array(
+            'groups' => array(),
+            'email' => 'saml-viewer@grafana.com',
+        ),
+    ),
+);