Add text banner to SAML System Console settings (#4195)

* Update saml_settings.jsx

* Update en.json

* Text tweak

* Fix build error

* Use classnames in saml_settings.jsx to fix build errors

webapp/components/admin_console/saml_settings.jsx

@@ -292,6 +292,14 @@ export default class SamlSettings extends AdminSettings {
 
         return (
             <SettingsGroup>
+                <div className='banner'>
+                    <div className='banner__content'>
+                        <FormattedMessage
+                            id='admin.saml.bannerDesc'
+                            defaultMessage='If a user attribute changes on the SAML server it will be updated the next time the user enters their credentials to log in to Mattermost. This includes if a user is made inactive or removed from a SAML Identity Provider. Remote logout with SAML servers is considered in a future release.'
+                        />
+                    </div>
+                </div>
                 <BooleanSetting
                     id='enable'
                     label={
@@ -541,4 +549,4 @@ export default class SamlSettings extends AdminSettings {
             </SettingsGroup>
         );
     }
-}
+}