[BUG] Incorrect Java version requirement in README for Vert.x 5

[sjw2547]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
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• What's the actual output vs expected output?
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Description

The README for Vert.x 5 states that Java 1.8+ is required, this should be Java 11+

openapi-generator version

7.22

Steps to reproduce

Build the Samples and check the README.md generated for Vert.x 5 projects

Suggest a fix

Create a specific mustache template for Java projects that selectively chooses the required Java version.