Debug hints on Account confirmation and password recovery

Please add the fact that in order for a forgot password email to be sent the user must `#1` exist in the DB and `#2 `the user must have EmailConfirmed Set to True. Also, if that is not the case there is no indication of that via the web interface, the email is never attempted to be sent.

I would like like to suggest that if env.IsDevelopment() is true that feedback be provided these requirments. - Thx

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#### Document Details

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* ID: fe1bea60-d173-f6d2-3559-b147699e295a
* Version Independent ID: 98e7aacb-2a01-d581-9b03-bfef2893163e
* Content: [Account confirmation and password recovery in ASP.NET Core](https://docs.microsoft.com/en-us/aspnet/core/security/authentication/accconfirm?view=aspnetcore-3.0&tabs=visual-studio#feedback)
* Content Source: [aspnetcore/security/authentication/accconfirm.md](https://github.com/aspnet/AspNetCore.Docs/blob/master/aspnetcore/security/authentication/accconfirm.md)
* Product: **aspnet-core**
* Technology: **aspnetcore-security**
* GitHub Login: @Rick-Anderson
* Microsoft Alias: **riande**