## Context

We recently identified a bug in the processing of events for pay in
advance charges that led to some duplicated fees in the database. See
#4220 for the fix of the initial
bug.

On the fees table, an index named
`idx_on_pay_in_advance_event_transaction_id_charge_i_16302ca167` was
supposed to prevent duplicated in advance fees:

```sql
CREATE UNIQUE INDEX idx_on_pay_in_advance_event_transaction_id_charge_i_16302ca167 ON public.fees 
USING btree (pay_in_advance_event_transaction_id, charge_id, charge_filter_id) 
WHERE ((created_at > '2025-01-21 00:00:00'::timestamp without time zone) 
  AND (pay_in_advance_event_transaction_id IS NOT NULL) 
  AND (pay_in_advance = true));
```

The issue reside in the way Postgres handles null values in indexes.
Each null value is considered a distinct value meaning the index is
useless in its current form as since `charge_filter_id` is null most of
the time...

## Goal

The main goal of the fix is to add a new set of index to really prevent
duplication in the database.
The difficulty will reside in the fact that we already have duplicated
values in DB and we cannot remove them as they have already impacted the
customers.

The complete fix will follow these steps:
- Phase 1:
- Add a new `duplicated_in_advance` flag on the fees table with default
value to false
  - Set this field to true for all existing duplicated fees
- Phase 2: 
- Add new indexes making preventing the duplication of fees making sure
that null values are not considered distinct and ignoring pre-existing
duplication
  - Remove the existing index 

## Description

This PR is the phase 1.
It adds two migrations to:
- Add the new `duplicated_in_advance` field to the fees table
- Fill the field for all existing duplicated fees