[Java][webclient/resttemplate] fix dependencies for gradle with jakarta enabled

Created by: ChristianMoesl

This PR fixes build errors, because of wrong dependencies in the gradle build templates for java clients with spring dependencies (webclient & resttemplate) and useJakartaEe enabled.

This error can be reproduced quite easily on master branch with the following commands:

cd samples/client/petstore/java/webclient-jakarta
chmod +x gradlew && gradle clean build

It will result in build errors like these:

What was done:

• remove swagger dependency, if it isn't in use
• use jakarta >= 2.0 if useJakartaEe is enabled (only jakarta 2.0 and above exposes annotations in jakarta.annotations.* namespace)
• use spring boot 3 and spring 6 for jakarta support
• added a Gradle build step to CI

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