[PDI-12812] - implementing exportResources for PMR.

The transformation could be referenced by repositoryReference, repositoryDir/File, or left out by the user. In any case, trans would be a non-null empty string. See how the combiner is conditionally retrieved  [here](https://github.com/kurtwalker/big-data-plugin/blob/60c820dfdf4d5178c6d4447b14b37449767f6a3d/src/org/pentaho/di/job/entries/hadooptransjobexecutor/JobEntryHadoopTransJobExecutor.java#L580)