feat: #1316 Single Table Inheritance pattern implemented (#2632)

* implemented single table inheritance

* added the Java documentation for the pattern

* updated code files as per the standards

* added the puml and png diagram for the file

* added README.md

* #1316 Single Table Inheritance pattern implemented

* resolved the Checkstyle violations

* removed the tests due to build failure

* updated the code as per review

* resolved Checkstyle violations

single-table-inheritance/src/main/java/com/iluwatar/entity/Truck.java

@@ -0,0 +1,38 @@
+package com.iluwatar.entity;
+
+import javax.persistence.DiscriminatorValue;
+import javax.persistence.Entity;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+/**
+ * A class that extends the PassengerVehicle class
+ * and provides the concrete inheritance implementation of the Car.
+ *
+ * @see TransportVehicle TransportVehicle
+ * @see Vehicle Vehicle
+ */
+@Data
+@NoArgsConstructor
+@Entity
+@DiscriminatorValue(value = "TRUCK")
+public class Truck extends TransportVehicle {
+
+  private int towingCapacity;
+
+  public Truck(String manufacturer, String model, int loadCapacity, int towingCapacity) {
+    super(manufacturer, model, loadCapacity);
+    this.towingCapacity = towingCapacity;
+  }
+
+  // Overridden the toString method to specify the Vehicle object
+  @Override
+  public String toString() {
+    return "Truck{ "
+            + super.toString()
+            + ", "
+            + "towingCapacity="
+            + towingCapacity
+            + '}';
+  }
+}