Action to publish DB layers in GeoServer (ds2dsGeoServerAction)

Here i share the action implemented in order to publish DB layers in GeoServer (#177). As requested, the action was implemented as part of the gb-action-ds2ds module. The implementation was discussed with @mbarto.

The action takes as event input the output of the ds2ds action.
If the workspace & datastore specified in the configuration do not exist they are created prior to the layer publication.

Looking forward to your feedback