Configure `CanGenerateTwoFactorTokenAsync` for default token providers

[arisliang]

I am trying to change PhoneNumberTokenProvider to not generate 2FA, but there seems to be no way to configure this currently in v2.1.

It would be good to be able to remove a token provider, so I could add a custom one back; or add option to override the 2FA generation flag for the default providers.

Alternatively I'm thinking to override the AddDefaultTokenProviders, which I'd rather not, because for my use, the rest of the default providers are fine.

[blowdart]

We've pretty much all but given up on phone auth as an industry, and it's not in our templates any more so it's unlikely we'd do much if any work on it any more.

@HaoK is there a reason we still add the 2fa provider by default?

[HaoK]

We generally just keep things the same for back compat, otherwise apps that were using phone 2fa all of a sudden would explode after upgrading

[arisliang]

Noted, I'm fine with what is it now. Will just use some workaround.