Correctly set the Java version in the README for Vert.x 5 project

[sjw2547]

…ects

Fixes #23697 - Set the Java version based on the Vert.x 5 flag

@bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger @karismann @Zomzog @lwlee2608 @martin-mfg

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Summary by cubic

Fixes #23697. Update Vert.x Java client READMEs to show the correct Java requirement: Vert.x 5 requires Java 11+ (Vert.x 3/4 remain Java 8+).

• Bug Fixes
  • Added Vert.x README template that sets the Java version based on the Vert.x 5 flag.
  • Updated samples/client/petstore/java/vertx5 and samples/client/petstore/java/vertx5-supportVertxFuture READMEs to Java 11+.

^{Written for commit c515aa0. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 76 files

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