Support protobuf data types in AtlasMap

If we want to have a data mapping connector for the managed kafka service we'll shortly need to support some more messaging specific data formats. This issue is to track implementing support for mapping data using the Protobuf data format.

Protobuf code generates Java classes for it's data types, so most likely the existing Java object support in AtlasMap should be sufficient, a lot of the work here will more likely be in the connector to ensure the correct documents are supplied to atlasmap at design/runtime.