feat: 2FA for admin mode

What does this MR do?

Add support for 2FA to admin mode feature. See screenshots below.

• Supports 2FA for both normal web authentication in gitlab and Omniauth authentication
• Created new concern Authenticates2FAForAdminMode making use of existing concern AuthenticatesWithTwoFactor
• Duplicated the views to support customization
• U2F has been tested with Krypton

Closes #35079 (closed)

🛠 with ❤ at Siemens

/cc @bufferoverflow @rpaik @ifarkas @reprazent

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team