Fix broken Java JUnit 4 quickstart HTTP client example

[Chandu0501]

Summary

• fix the Java/JUnit 4 quickstart snippet to use wireMockRule.url(...) instead of the undefined wiremockServern- make the Java 11+ HTTP client example compile by using URI.create(...), hrows Exception, and HttpRequest.BodyPublishers.noBody()n
  Closes Issue on Quick Start: API Mocking with Java and JUnit 4 #307.

Verification

• pnpm build generated /docs/quickstart/java-junit/index.html, then failed in the repo's existing copy-static-homepage build hook with ENOENT while copying src/static/index.html to an invalid C:\C:... destination
• mvn -q test passed in a throwaway verification project that exercises the corrected JUnit 4 snippet against WireMock 3.13.2