Add: UnknownRequestException class to throw when encountering unknown request type

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/network/command/UnknownRequestException.java

@@ -0,0 +1,14 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.network.command;
+
+public class UnknownRequestException extends RuntimeException {
+    private final String requestName;
+
+    public UnknownRequestException(String message, String requestName) {
+        this.requestName = requestName;
+        super(message);
+    }
+
+    public String getRequestName() {
+        return requestName;
+    }
+}