Add new user field for totp secret

src/invidious/user/user.cr

@@ -7,6 +7,7 @@ struct Invidious::User
   property notifications : Array(String)
   property subscriptions : Array(String)
   property email : String
+  property totp_secret : String?
 
   @[DB::Field(converter: Invidious::User::PreferencesConverter)]
   property preferences : Preferences

src/invidious/users.cr

@@ -17,6 +17,7 @@ def create_user(sid, email, password)
     token:             token,
     watched:           [] of String,
     feed_needs_update: true,
+    totp_secret:       nil,
   })
 
   return user, sid