Add: CheckUsernameRequest containing username to check for availability

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/commands/check_nick/CheckUsernameRequest.java

@@ -0,0 +1,17 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.commands.check_nick;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.Request;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.RequestContext;
+
+public class CheckUsernameRequest extends Request {
+    private final String username;
+
+    public CheckUsernameRequest(RequestContext context, String username) {
+        super(context);
+        this.username = username;
+    }
+
+    public String getUsername() {
+        return username;
+    }
+}