Rename the Gradle plugin to io.quarkus

[Sanne]

while at it, flipped the build to use the java-gradle-plugin which simplifies creation (and validation!) of the plugin metadata, and enabled the build scanner - also useful to identify further issues.

[stalep]

looks good! i was just wondering if mavenLocal() is needed since its fetching from the target folders?

[Sanne]

@stalep thanks :)

Indeed mavenLocal() isn't needed, but it allows to re-use the downloaded stuff for all transitive dependencies. I wouldn't use it in a Gradle build but it's kinda useful in this case.