Refactor: Convert PluginPropertiesExtension to Java (#34459)

[fabiodrg]

This is the first time I am working at this level with Gradle, so I went through some challenges. One of them is not yet solved, which is how to access the extra properties from Project. Whenever I try to compile it fails saying the ext symbol is not defined (project.ext).
I am looking into Gradle documentation for days, and I can't find a workaround for this. I was having similar issues when accessing properties such version or name, but I could solve it buy using the methods available. Probably I am misunderstanding how this works. If anyone could provide some help, I would appreciate it a lot.

Due the problem with accessing the extra properties, the following methods are not completed, but they aren't used at the moment, so I decided to create the pull request anyway, and hopefully with the community and elastic team insights I will be able to complete this task.

• setLicenseFile()
• setNoticeFile()

[alpar-t]

@fabiodrg666 project.ext in java is project.getExtensions() .getByType(ExtraPropertiesExtension.class). Missing properties on a project are looked up from a number of places, extensions are among those, and ext is a special extension of type ExtraPropertiesExtension. I do think the setters are used. note that Groovy calls setters on assignment if they are available.

[elasticmachine]

Pinging @elastic/es-core-infra

[rjernst]

In groovy, the Input annotation adds the get/set capabilities, and is automatically tracked. However, that is for tasks. I'm not sure it actually makes sense (and was erroneous but harmless in the old groovy code). @atorok can you confirm my understanding? If so, I think all these Input annotations should be removed.

[alpar-t]

That's right, the annotations don't do anything on extensions, their for tasks and need to be placed on the getter method in Java ( having them on properties works on Groovy only )

[fabiodrg]

Thanks for your feedback, I will remove the Input annotations.

[danielmitterdorfer]

@fabiodrg666 are you still interested in getting this PR in?

[alpar-t]

Overlaps with #39605

[alpar-t]

@fabiodrg666 I'm going to close this, please reopen if you plan to work on it