Remove the release/java11 branch

[arey]

The Dockerfile is now based on java11: https://github.com/spring-petclinic/spring-petclinic-microservices/blob/master/docker/Dockerfile
The release/java11 branch and the readme.md have to be delete / update.
See the issue #190

[charboubmustapha]

it make sens to move to Java 11 as default JVM and probably another release branch with Java 17

[arey]

Spring Boot 3 supports Java as a baseline so we have to remove the release/java11 branch.

[arey]

Deleted this day