Publish the plugin with a domain for uniqueness and make available on Gradle plugin portal

[bmuschko]

Expected Behavior

The published plugin should live under com.bmuschko:gradle-kubernetes-plugin on JCenter.

Current Behavior

The published plugin on JCenter is only available under the namespace gradle-kubernetes-plugin. There could be other kubernetes plugins if linked to the Gradle Plugin Portal.

@cdancy I am not sure if we can just rename the package on JCenter? Would that break something on your end?

Context

Provide a unique namespace for the plugin to make it compatible with the Gradle Plugin Portal.