Usage of class JavaPluginConvention should be replaced with JavaPluginExtension

[bmuschko]

Issue Description

You are using the class JavaPluginConvention in a Gradle task implementation. This class has been deprecated and will be removed from Gradle's API soon. All consumers of Gradle version's that removed the class will break.

From the Gradle API:

Deprecated.
Replaced by JavaPluginExtension. This class is scheduled for removal in Gradle 9.0.
Is mixed into the project when applying the JavaBasePlugin or the JavaPlugin.

Steps to Reproduce

Apply Gradle plugin, run with --warning-mode all.

Expected Result

No warning message is rendered for plugin.

Actual Result

When build is run with --warning-mode all, the corresponding warning message is rendered.

Your Environment and Setup

• graphql-java-codegen version: v5.7.1
• Build tool: Gradle 8.0

[bmuschko]

Is this something you are planning to fix soon or would you rather want to receive a pull request?

[kobylynskyi]

There is already a PR created by @esfomeado for the same.
Can you take a look at it as let me know if the fix looks good to you as well?
Thanks

[bmuschko]

@kobylynskyi Perfect. LGTM!