Expose jclouds-core for the Branch API

[martinda]

The Branch api exposes com.google.gson.JsonElement, and it comes from jclouds-core transitively:

compileClasspath - ...
+--- org.apache.jclouds:jclouds-core:2.5.0
|    +--- com.google.code.gson:gson:2.8.9

I think the right solution is to declare a direct api dependency on com.google.code.gson:gson:2.8.9 since this library uses an instance of that library via a type declaration in a data type that users are expected to use.

Exposing all of jclouds-core might be excessive, but I have not reviewed the whole list of APIs yet.

This issue is in response to the question asked in cdancy/artifactory-rest#88 (comment)

[martinda]

The find-class-gradle-plugin is proving useful to find the dependency that brings a given class.