Add 'linked' option to 'autoRegisterFloodgate'

This makes sense with Floodgate 2.0's Global Link API

core/src/main/java/com/github/games647/fastlogin/core/shared/FloodgateManagement.java

@@ -105,7 +105,7 @@ public abstract class FloodgateManagement<P extends C, C, L extends LoginSession
             }
         }
 
-        if (!isRegistered && autoRegisterFloodgate.equals("false")) {
+        if (!isRegistered && !isAutoRegisterAllowed()) {
             return;
         }
 
@@ -120,6 +120,17 @@ public abstract class FloodgateManagement<P extends C, C, L extends LoginSession
 
     }
 
+    /**
+     * Decude if the player can be auto registered.
+     * The config option 'non-conflicting' is ignored by this function.
+     * @return true if the Player can be registered automatically
+     */
+    private boolean isAutoRegisterAllowed() {
+        return autoRegisterFloodgate.equals("true") 
+                || autoRegisterFloodgate.equals("no-conflict") // this was checked before
+                || (autoRegisterFloodgate.equals("linked") && isLinked);
+    }
+
     /**
      * Decides wether checks for conflicting Java names should be made
      * @return ture if an API call to Mojang is needed

core/src/main/resources/config.yml

@@ -234,6 +234,7 @@ allowFloodgateNameConflict: false
 # Possible values:
 #   false: Disables auto registering for every player connecting through Floodgate
 #   true: Enables auto registering for every player connecting through Floodgate
+#   linked: Only Bedrock accounts that are linked to a Java account will be registered automatically
 #   no-conflict: Bedrock players will only be automatically registered if the Mojang API reports
 #     that there is no existing Premium Java MC account with their name.
 #     This option can be useful if you are not using 'username-prefix' in floodgate/config.yml