feat: implement Remote Procedure Invocation pattern (#2680)

[dileep98]

• Add RPI pattern demonstrating REST-based synchronous communication
• Implement RpiService (Spring Boot REST controller)
• Implement RpiClient (using RestTemplate)
• Add comprehensive unit and integration tests
• Add UML diagram and README documentation
• Resolves Microservice pattern: Remote procedure invocation #2680

Pull Request Template

What does this PR do?

This PR implements the Remote Procedure Invocation (RPI) design pattern, demonstrating synchronous request/reply communication between microservices using REST over HTTP.

Implementation Details:

• RpiService: Spring Boot REST controller exposing a /greet endpoint
• RpiClient: Client using RestTemplate to make synchronous HTTP calls
• App: Spring Boot application entry point with pattern explanation
• Comprehensive unit and integration tests with Spring Boot Test and Mockito
• UML class diagram showing the pattern structure
• Complete README with YAML front matter, examples, and documentation

Pattern Characteristics:

• Synchronous communication with blocking request/reply
• Direct client-to-service communication (no message broker)
• Simple HTTP/REST protocol implementation
• Demonstrates tight runtime coupling and availability considerations

Fixes #2680

[github-actions]

PR Summary

Adds a complete Remote Procedure Invocation pattern module demonstrating synchronous REST-based communication between microservices. Includes RpiService (Spring Boot REST controller), RpiClient (RestTemplate-based client), application bootstrap, comprehensive tests, UML diagram, and README documentation. Updates root POM to include the new module and centralizes dependencies for Spring Boot and testing.

Changes

File	Summary
modified: pom.xml	Updated the root POM to include the new remote-procedure-invocation module, reorganized dependency management for Spring Boot and testing, added Lombok handling, and expanded module and repository declarations.
added: remote-procedure-invocation/README.md	Introduces the Remote Procedure Invocation pattern with overview, usage, and architectural details. Documents server (RpiService), client (RpiClient), tests, UML diagram, and README front matter.
added: remote-procedure-invocation/etc/rpi.urm.png	New UML diagram image illustrating the RPI pattern structure used by the README.
added: remote-procedure-invocation/etc/rpi.urm.puml	PlantUML diagram defining App, RpiService, and RpiClient with their relationship and HTTP interaction.
added: remote-procedure-invocation/pom.xml	Module pom declaring Spring Web and Test dependencies, JUnit engine for tests, and an assembly plugin to create a fat jar with com.iluwatar.rpi.App as the main class.
added: remote-procedure-invocation/src/main/java/com/iluwatar/rpi/App.java	Spring Boot application entry point for the RPI module with a test-friendly shutdown when using the 'test' argument.
added: remote-procedure-invocation/src/main/java/com/iluwatar/rpi/RpiClient.java	Client-side component using RestTemplate to call the remote service's /greet endpoint and return the response, with logs.
added: remote-procedure-invocation/src/main/java/com/iluwatar/rpi/RpiService.java	Server-side REST controller exposing /greet endpoint that returns a greeting for the given name (default 'World').
added: remote-procedure-invocation/src/test/java/com/iluwatar/rpi/AppTest.java	Tests the RPI module startup, default/custom greetings, and RpiClient invocation against the service.
added: remote-procedure-invocation/src/test/java/com/iluwatar/rpi/RpiClientTest.java	Unit test for RpiClient using a mocked RestTemplate to verify the greeting response.
added: remote-procedure-invocation/src/test/java/com/iluwatar/rpi/RpiServiceTest.java	Unit tests for RpiService ensuring correct greetings for specific and default names.

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