option to migrate umwl_external_data_* to managed_external_data_*

[fajabird]

As part of our routine to merge data from unmanaged workloads (which we import from CMDB and assign a umwl_external_data_set and ref) to our VENs we would like to maintain the external_data_set and reference, thus running below script should end up with umwl_external_data* and managed_external_data_* containing the same set of information. Currently managed_external_data_* is empty.

Script:
workloader umwl-cleanup --output-file $FILE
workloader wkld-import $FILE

current result of running umwl-cleanup (only relevant columns and for a signle umwl/ven pair):
managed_external_data_set,managed_external_data_ref,umwl_external_data_set,umwl_external_data_ref
,,script/CMDB,ab0b93461b27d19039b71065bb4bcbc1

expected result:
managed_external_data_set,managed_external_data_ref,umwl_external_data_set,umwl_external_data_ref
script/CMDB,ab0b93461b27d19039b71065bb4bcbc1,script/CMDB,ab0b93461b27d19039b71065bb4bcbc1