Add OkHttp GetExample with Maven project structure

[Copilot]

Adds the OkHttp GetExample.java sample demonstrating HTTP GET requests.

Changes

• Java project structure: Created samples/guide/src/main/java/okhttp3/guide/ following Maven conventions
• GetExample.java: Added OkHttp client example with improvements:
  • Updated URL from deprecated raw.github.com to raw.githubusercontent.com
  • Added null check for response.body() to prevent NPE
• Maven configuration: Added pom.xml with OkHttp 4.12.0 dependency
• Build configuration: Added .gitignore for Java/Maven artifacts

String run(String url) throws IOException {
  Request request = new Request.Builder().url(url).build();
  
  try (Response response = client.newCall(request).execute()) {
    if (response.body() == null) {
      throw new IOException("Response body is null");
    }
    return response.body().string();
  }
}

Project compiles cleanly with Maven. No security vulnerabilities detected in dependencies.

Original prompt

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This section details on the original issue you should resolve

<issue_title>raw.githubusercontent.com/square/okhttp/master/samples/guide/src/main/java/okhttp3/guide/GetExample.java

</issue_title>
<issue_description>https://raw.githubusercontent.com/square/okhttp/master/samples/guide/src/main/java/okhttp3/guide/GetExample.java</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes eternograf/AlfazetOperations#1

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