Set Java11 as minimal version

[abelsromero]

Kind of change

• [ ] Bug fix
• [ ] New non-breaking feature
• [x] New breaking feature
• [ ] Documentation update
• [x] Build improvement

Description

What is the goal of this pull request?

Remove support for Java 8 and set 11 as de minimal version. Java8 is EOL and I don't think we should promote using it.

How does it achieve that?

• Remove use of 'task.options.release' for Java version configuration in favour of Gradle's preferrs 'toolchain'.
• Removed Java 8 from pipelines. Also:
• Bump Gradle to latest v8.0.2
• Remove use of 'io.spring.dependency-management' Gradle plugin in 'spring-boot' app in favor of Gradle's BOM support. This reduces maintenance since only Boot version needs to be updated.
• Enables CI pipelines for Java 19 on macos and Windows.

Are there any alternative ways to implement this?

task.options.release still works, but Gradle docs suggest using the new toolchain configuration as this is the "preferred".

Are there any implications of this pull request? Anything a user must know?

Users using Java 8 should stay in 2.5.x until they upgrade their apps.

Issue

If this PR fixes an open issue, please add a line of the form:

Fixes #1150

Release notes

Please add a corresponding entry to the file CHANGELOG.adoc

[abelsromero]

Should we create a "Breaking changes" section in the CHANGELOG? I think it'd make the release notes much more simple when the time comes.

[abelsromero]

Running tests in my repo to see if we can find a workaround for the Windows+Java17 issue.

[abelsromero]

Fixed the issue by forcing the toolchain version manually on Windows builds ONLY. It's sad but simple enough that with a simple comment, we can monitor it and remove it if it ever gets fixed. I am also keeping it in a separate commit, since AsciidoctorJ uses "merge pr" that will also make things easier to track.

Since the release pipeline runs already on Java 11, there won't compatibility issues. The release will be 100% J11 binary.