Purpose
=======
Add more fields when we merge multiple leads to be sure not lose
valuable information.

Specifications
==============
Those fields are propagated to the destination if the value on the
destination is Falsy
- referred
- color
- recurring_revenue
- recurring_plan
- function
- lang_id
- date_deadline
- reveal_id
- lead_mining_request_id
- reveal_ip
- reveal_iap_credits
- reveal_rule_id
- event_lead_rule_id
- event_id

The "lost_reason" field is propagated to the destination only if it's
lost (otherwise, it makes no sense to have a lost reason on a non-lost
lead).

The field "iap_enrich_done" is set to True if at least one lead has been
enriched.

We also keep the sum of all the lead tags (and remove any potential
duplicates).

The address is taken from the lead with the most non-empty address
fields (sorted by highest rank if multiple lead have the same amount
of non-empty fields).

Task-2447721
PR odoo/odoo#75742