Add support for app Icon

[Cloudmersive]

TOTP supports showing an icon next to an authentication item, for example in Microsoft Authenticator you can see the GitHub icon next to the GitHub item.

Request: Add support for this.

[RobThree]

Do you have a pointer where this icon is documented? It's not mentioned in the Key Uri format. I did find this but AFAIK it's not very widely supported (as is also stated in that answer: "It's not part of the spec for TOTP, although it should be.").

Is it really in the QR code or is it simply retrieving a <site>.com/favicon.ico or something using some "magic" where the domain is extracted from the <user>@<domain> part?

Also: I'm not sure if one would want to support such a feature; it would allow for (some) tracking of users/apps which might not be desirable.