[passport] Add username property to profile

The profile data usually contains a username. Here are some strategies that implement it: [facebook](https://github.com/jaredhanson/passport-facebook/blob/master/lib/profile.js#L15) and [github](https://github.com/jaredhanson/passport-github/blob/master/lib/profile.js#L16).

passport/passport.d.ts

@@ -58,6 +58,7 @@ declare module 'passport' {
             provider: string;
             id: string;
             displayName: string;
+            username?: string;
             name?: {
                 familyName: string;
                 givenName: string;