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]
------
[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>

enterprise/app/controllers/api/v1/accounts/saml_settings_controller.rb

@@ -1,4 +1,5 @@
 class Api::V1::Accounts::SamlSettingsController < Api::V1::Accounts::BaseController
+  before_action :check_saml_sso_enabled
   before_action :check_saml_feature_enabled
   before_action :check_authorization
   before_action :set_saml_settings
@@ -53,4 +54,10 @@ class Api::V1::Accounts::SamlSettingsController < Api::V1::Accounts::BaseControl
 
     render json: { error: I18n.t('errors.saml.feature_not_enabled') }, status: :forbidden
   end
+
+  def check_saml_sso_enabled
+    return if GlobalConfigService.load('ENABLE_SAML_SSO_LOGIN', 'true').to_s == 'true'
+
+    render json: { error: I18n.t('errors.saml.sso_not_enabled') }, status: :forbidden
+  end
 end