feat: Control the allowed login methods via Super Admin (#12892)

- Control the allowed authentication methods for a chatwoot installation
via super admin configs. [SAML, Google Auth etc]
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[Codex
Task](https://chatgpt.com/codex/tasks/task_e_6917d503b6e48326a261672c1de91462)

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Co-authored-by: Pranav <pranav@chatwoot.com>
Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>

app/helpers/super_admin/features.yml

@@ -9,6 +9,13 @@ captain:
   icon: 'icon-captain'
   config_key: 'captain'
   enterprise: true
+saml:
+  name: 'SAML SSO'
+  description: 'Configuration for controlling SAML Single Sign-On availability'
+  enabled: <%= ChatwootApp.enterprise? %>
+  icon: 'icon-lock-line'
+  config_key: 'saml'
+  enterprise: true
 custom_branding:
   name: 'Custom Branding'
   description: 'Apply your own branding to this installation.'