fix: update elasticsearch docker image version to 8.15.2

[tpreviero]

Since the elasticsearch docker image version 8.13.2 is not available anymore (as discovered during fastify/fastify-elasticsearch#118) updates the image to 8.15.2 version.

Checklist

• run npm run test and npm run benchmark no tests
• tests and/or benchmarks are included no tests
• documentation is changed or added no documentation
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct