Merge and replace actions for reporting assets

If a reporting asset with the same identity exists in the target repository, then the new asset is merged with the existing asset.

A reporting asset has various attributes, and the merging process affects the attributes differently. A reporting asset has the following attributes:

Report design: If a matching report exists in the target repository, the report is overwritten provided that the user importing the asset has update permission on the target report. Otherwise the import of that asset fails.
Report access control list: The access control list for the target report is retained.
Report results: Report results cannot change, and so a report result in an import file will not overwrite the target report result.
FavoriteUsers: If the report exists on the target and has a FavoriteUsers list, the imported FavoriteUsers list is merged with the existing list. Any users that the imported list contains are added to the list of the target report.