[IATI] insert namespace to provide a UID for each result and indicator

[stevieflow]

On conversion insert a namespaced UID into each result and indicator.

In doing this, we will then be able to flatten these elements out

This may be applied as a setting / switch for the user - switching it on (or off) as deflaut - TBD

[rorads]

Hello!

For a little extra context, this is how I've worked around this issue with the existing behaviour: https://docs.google.com/spreadsheets/d/1ZMxFME4krHMxrqpFJS68ecXIppmwAuYYHA4ZP7V4zdE/edit?usp=sharing

This adds an <iati-identifier> as a child element for each result, with a unique identifier placed there for each result. This then allows CoVE to use the same id merging logic from ocds / 360 land. The admin that's required after is to delete these elements to make the file valid with the IATI xsd.

So having something like <cove:uid>1234567</cove:uid> (ala this page) could work well, as long as it gets preserved on reverse conversion as well.