feat: MFA (#12290)

## Linear:
- https://github.com/chatwoot/chatwoot/issues/486

## Description
This PR implements Multi-Factor Authentication (MFA) support for user
accounts, enhancing security by requiring a second form of verification
during login. The feature adds TOTP (Time-based One-Time Password)
authentication with QR code generation and backup codes for account
recovery.

## Type of change

- [ ] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

- Added comprehensive RSpec tests for MFA controller functionality
- Tested MFA setup flow with QR code generation
- Verified OTP validation and backup code generation
- Tested login flow with MFA enabled/disabled

## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: Pranav <pranav@chatwoot.com>
Co-authored-by: Sojan Jose <sojan@pepalo.com>
Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

config/locales/en.yml

@@ -103,6 +103,18 @@ en:
       invalid_value: Invalid value. The values provided for %{attribute_name} are invalid
     custom_attribute_definition:
       key_conflict: The provided key is not allowed as it might conflict with default attributes.
+    mfa:
+      already_enabled: MFA is already enabled
+      not_enabled: MFA is not enabled
+      invalid_code: Invalid verification code
+      invalid_backup_code: Invalid backup code
+      invalid_token: Invalid or expired MFA token
+      invalid_credentials: Invalid credentials or verification code
+      feature_unavailable: MFA feature is not available. Please configure encryption keys.
+  profile:
+    mfa:
+      enabled: MFA enabled successfully
+      disabled: MFA disabled successfully
     account_saml_settings:
       invalid_certificate: must be a valid X.509 certificate in PEM format
   reports: