detekt-gradle-plugin has two publishing configuration

[cortinico]

On a related note - I've published my own fork in our local Artifactory which is configured strictly, i.e. it does not allow re-uploads of the same artifact version. When running the publish task on the detekt-gradle-plugin module, Gradle told me

Multiple publications with coordinates 'io.gitlab.arturbosch.detekt:detekt-gradle-plugin:1.12.0-RC1-android-gradle-plugin' are published to repository 'maven'. The publications will overwrite each other!

and the upload promptly failed because of that. I couldn't figure out myself what was different for this module with respect to the others, where no such warning is spit out and the initial upload works, I could only suspect that the com.gradle.plugin-publish plugin used in this module eventually adds another publishing configuration, but I don't know nearly enough about this plugin to verify that is true.

Originally posted by @realdadfish in #2995 (comment)

I couldn't figure out myself what was different for this module with respect to the others, where no such warning is spit out and the initial upload works, I could only suspect that the com.gradle.plugin-publish plugin used in this module eventually adds another publishing configuration, but I don't know nearly enough about this plugin to verify that is true.

I've done early investigation and that's exactly the case. The publish-plugin adds another configuration. Specifically:

$ ./gradlew detekt-gradle-plugin:tasks | grep ToBintrayRepository
publishAllPublicationsToBintrayRepository
publishDetektPluginPluginMarkerMavenPublicationToBintrayRepository <- Added by `publish-plugin`
publishDetektPublicationPublicationToBintrayRepository             <- Added by us (packaging)
publishPluginMavenPublicationToBintrayRepository.                  <- Added by `publish-plugin`

Specifically the last two publications have the same maven coordinates. We should make sure one of the two is excluded.

[arturbosch]

Actually I'm not sure if my PR breaks publishing to Gradle plugin portal itself xD but it deduplicates the publications.
Edit: well it shouldn't because pluginBundle has it own mavenCoordinates.

[cortinico]

Actually I'm not sure if my PR breaks publishing to Gradle plugin portal itself xD

It shouldn't. I tried to publishPlugin and it failed with a 403 (that is expected):

> Task :detekt-gradle-plugin:publishPlugins FAILED
Publishing plugin io.gitlab.arturbosch.detekt version 1.12.0-RC1

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':detekt-gradle-plugin:publishPlugins'.
> Unauthorized!

If we see something wrong for the upcoming version release, we know what's the culprit