Use upstream alpine image

[wkoot]

As detailed in https://github.com/SonarSource/docker-sonarqube/issues/652, there might be an alpine image soon.
Switch to this upstream container if possible

[wkoot]

Looks like the upgrade to Java 21 is delayed, now expected to be in SonarQube 10.5:
https://community.sonarsource.com/t/when-do-you-plan-to-support-the-java-21-lts-for-the-sonar-maven-plugin/102106/15