Gradle plugin: fix --include-build workflow

By convention, gradle uses project name as artifactId, `project.group`
property for groupId and `project.version` for version.

This commit switches to this convention instead of configuring
publication tasks directly. It allows to easily substitute published
plugin with a plugin build locally by issuing

`./gradlew build --include-build ../kotlin-native`

in the dependent project.

settings.gradle

@@ -25,4 +25,4 @@ include ':runtime'
 include ':common'
 include ':backend.native:tests'
 include ':tools:helpers'
-include ':tools:gradle-plugin'
+include ':tools:kotlin-native-gradle-plugin'