Fix Gradle Plugin Portal badge (#5067)

This is a little hacky, because the maven & plugin portal shields
often don't report the correct version: badges/shields#6188

Instead, we use the Maven Central method, which should have
the same version published as the Gradle Plugin Portal does.

README.md

@@ -3,7 +3,7 @@
 [![Join the chat at #detekt on KotlinLang](https://img.shields.io/badge/%23detekt-on_slack-red.svg?logo=slack)](https://kotlinlang.slack.com/archives/C88E12QH4)
 [![Visit the website at detekt.dev/](https://img.shields.io/badge/visit-website-red.svg?logo=firefox)](https://detekt.dev/)
 [![Maven Central](https://img.shields.io/maven-central/v/io.gitlab.arturbosch.detekt/detekt-cli?label=MavenCentral&logo=apache-maven)](https://search.maven.org/artifact/io.gitlab.arturbosch.detekt/detekt-cli)
-[![Gradle Plugin](https://img.shields.io/maven-metadata/v/https/plugins.gradle.org/m2/io/gitlab/arturbosch/detekt/io.gitlab.arturbosch.detekt.gradle.plugin/maven-metadata.xml.svg?label=Gradle&logo=gradle)](https://plugins.gradle.org/plugin/io.gitlab.arturbosch.detekt)
+[![Gradle Plugin](https://img.shields.io/maven-central/v/io.gitlab.arturbosch.detekt/detekt-gradle-plugin?label=Gradle&logo=gradle)](https://plugins.gradle.org/plugin/io.gitlab.arturbosch.detekt)
 [![Revved up by Gradle Enterprise](https://img.shields.io/badge/Revved%20up%20by-Gradle%20Enterprise-06A0CE?logo=Gradle&labelColor=02303A)](https://ge.detekt.dev/scans)
 
 ![Pre Merge Checks](https://github.com/detekt/detekt/workflows/Pre%20Merge%20Checks/badge.svg?branch=main)