docs: modernize Gradle dependency setup in basic sample - #11307

Which Issue(s) This PR Fixes

No linked issue. This corrects the dependency setup in the basic sample documentation.

Brief Description

The basic sample uses the compile dependency configuration, which was removed in Gradle 7. Replace it with implementation and include the Java plugin, Maven Central repository, and dependencies block so readers can use the example in build.gradle.

Label the Maven snippet as XML and the Gradle snippet as Groovy. The client dependency version and all producer/consumer examples remain unchanged.

Reference: https://docs.gradle.org/current/userguide/upgrading_version_6.html#sec:configuration_removal

How Did You Test This Change?

• Parsed the Maven dependency snippet as XML and verified its coordinates.
• Verified that all send/consume examples are unchanged.
• Ran git diff --check successfully.
• Gradle execution was not performed because Gradle is not installed locally.

Prepared with AI assistance and checked as described above.