Description of problem: It would be great to mplement a new action (add_mapping_item) for transformation mapping, that adds a new transformation mapping item to previously created transformation mapping.
https://github.com/ManageIQ/manageiq-api/pull/546
Using the steps given on the PR : https://github.com/ManageIQ/manageiq-api/pull/546 I was able to create and then add_items to Infra mappings using transformation_mappings api for CFME Version: 5.11.0.11.20190625161125_392c61e