Add Kotlin DSL in package registry docs

Yongshun Yerequested to merge
huanshankeji-open-source/gitlab:doc-package-registry-maven-gradle-kotlin-dsl into master

What does this MR do and why?

This MR adds the Gradle Kotlin DSL in the docs to configure Gradle for the Maven repositories in GitLab package registries, to make it easier to configure the Gradle build scripts for users using the Gradle Kotlin DSL.

Screenshots or screen recordings

None.

How to set up and validate locally

I don't think it's needed for docs.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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