Add rest-client-test module: @RestClientTest on Boot 4.1, Jackson 3 by default, and the RestClient-vs-RestTemplate root-URI matching trap (post #49)

rest-client-test/src/main/java/com/ankurm/restclienttest/Employee.java

@@ -0,0 +1,7 @@
+package com.ankurm.restclienttest;
+
+/**
+ * Immutable DTO for the employee data returned by the (simulated) external HR system's API.
+ */
+public record Employee(Integer id, String firstName, String lastName, String email) {
+}