[Hardening] F-02: Default Configuration Forces User’s Posture to Password-Only.

### The required feature described as a wish

**Description:** the global configuration setting `enable.user.2fa` defaults to False, meaning users who wish to use two-factor authentication (2FA) cannot do so without a Root Admin first enabling the setting and restarting the management server(s).

**Affected Components:** Management UI

**Impact:** Any compromised or weak user credential is sufficient to gain full access to a user's CloudStack account. This makes the platform susceptible to credential-stuffing, phishing, and brute-force attacks with no second factor to impede unauthorized access.

**Steps to Reproduce:**
- Log in to the CloudStack Management UI as a Root Admin.
- Navigate to Configuration > Global Settings.
- Search for `enable.user.2fa` and observe that its value is set to False.
- Attempt to enable 2FA on your own user account, and confirm that it is not permitted.

**Recommended Remediation:** Change the default value of `enable.user.2fa` to True so that users are always permitted to enroll in 2FA without requiring Root Admin intervention.

Management UI の Global Settings における enable.user.2fa の処理から始め、そのデフォルト値がユーザー登録をどのように制御するかを確認します。デフォルト値によって、Root Admin の介入や management-server の再起動なしにユーザーが 2FA に登録できるようになれば、変更は完了です。UI で設定と登録フローを確認してください。

索引モデルが issue の本文から書いたものです。