configTar task requires java plugin to be applied

[jmcampanini]

// technically it needs the java-base plugin

issue

when attempting to publish a publication with configTar as an artifact, gradle throws an error that the file is not present, since the file is JUST the extension:

> Failed to publish publication 'config' to repository 'maven-config'
   > Invalid publication 'config': artifact file does not exist: '.asset.config.tgz'

considering we're:

• not setting default values using java plugin
• not setting the values in configTar

we're ending up producing a filename that's just the extension due to the AbstractArchiveTask::getArchiveName method

the gradle docs even include information about applying the java plugin:

Why are you using the Java plugin?

The Java plugin adds a number of default values for the archive tasks. You can use the archive tasks without using the Java plugin, if you like. You will need to provide values for some additional properties.

proposed fixes:

• A. apply the java-base plugin in the config plugin. considering the primary (but not only) audience of the config tar task is java applications, this isn't horrible
• B. fully configure the file name of the configTar task, similar to how the distTar task does it

[jmcampanini]

seems that this is related to #203