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>

app/models/super_admin.rb

@@ -7,6 +7,7 @@
 #  confirmation_sent_at   :datetime
 #  confirmation_token     :string
 #  confirmed_at           :datetime
+#  consumed_timestep      :integer
 #  current_sign_in_at     :datetime
 #  current_sign_in_ip     :string
 #  custom_attributes      :jsonb
@@ -17,6 +18,9 @@
 #  last_sign_in_ip        :string
 #  message_signature      :text
 #  name                   :string           not null
+#  otp_backup_codes       :text
+#  otp_required_for_login :boolean          default(FALSE), not null
+#  otp_secret             :string
 #  provider               :string           default("email"), not null
 #  pubsub_token           :string
 #  remember_created_at    :datetime
@@ -33,10 +37,12 @@
 #
 # Indexes
 #
-#  index_users_on_email                 (email)
-#  index_users_on_pubsub_token          (pubsub_token) UNIQUE
-#  index_users_on_reset_password_token  (reset_password_token) UNIQUE
-#  index_users_on_uid_and_provider      (uid,provider) UNIQUE
+#  index_users_on_email                   (email)
+#  index_users_on_otp_required_for_login  (otp_required_for_login)
+#  index_users_on_otp_secret              (otp_secret) UNIQUE
+#  index_users_on_pubsub_token            (pubsub_token) UNIQUE
+#  index_users_on_reset_password_token    (reset_password_token) UNIQUE
+#  index_users_on_uid_and_provider        (uid,provider) UNIQUE
 #
 class SuperAdmin < User
 end