[Feature Request] Format options for Code-based MFA Support

**Is your feature request related to a problem? Please describe.**
openvpn with activated totp (static-challenge "TOTP Code" 1) is sending the password in the format "\\" (no semicolon, no space, plain totp code with password in one string)

If using authentik as backend with activated option "Code-based MFA Support", authentik expects the string to be "totp;password"

**Describe the solution you'd like**
The option "Code-based MFA Support" having options on how the string is formatted for better support for other service providers. I'm sure other Services are having different formats aswell.
Having multiple options for the format would be nice.
```
1. ;
2. ;
3.
4.
```

**Describe alternatives you've considered**
The only alternative for this is to have the option 'static-challenge "TOTP Code" 1' on a openvpn client not enabled.
that way the user doesn't get a prompt for a TOTP key. (just the password prompt)
The user now needs to input his password followed by a semicolon and the totp code

**Additional context**
The alternative is just not user-friendly.
Openvpn GUI has the feature to display an input field for the totp code but the way authentik can be used in opnsense in this example renders that input field useless as authentik expects the string to be in another format that in my knowlege cannot be changed on openvpn GUI's side.

I'm happy to provide more details if my description is not understood well enough