Merging duplicates with orgsharing: Resolve duplicate custom fields

[niklasva82]

Custom fields are different between different organizations, which means that any merge of people on a top level will have to be able choose between potential duplicate values of custom fields in all sub-organizations.

Example:
Organization schema:
Org 1 --> Org 2
|--> Org 3

Org 3 has the custom field entry date, Org 2 has the custom field extra notes.

John Smith has entry date value '2020-10-01' and John Smith's duplicate has the value '2019-05-01'. Both versions of John Smith have different notes in the extra notes field in Org 3.

The admin in Organization 1 now wants to merge the two John Smith's into a sinlge John Smith. We have to recursively fetch any fields and their values for sub-organizations and display them to the admin to choose which one should be used in the new single John Smith.