Merged PR 4224: Rework accounting aggregations for Financial Reporting

# Description

This PR reworks the Financial Aggregations based on Nathan's requirements, that can be found in an Excel attached to the board ticket.

Main changes:
- Accounting seed now contains 3 financial aggregations as requested by Finance
- These 3 aggregations are propagated up to reporting. This effectively breaks a WIP report - but it's WIP, not in prod, so it's not a big deal

# Checklist

- [X] The edited models and dependants run properly with production data.
- [X] The edited models are sufficiently documented.
- [X] The edited models contain PK tests, and I've ran and passed them.
- [X] I have checked for DRY opportunities with other models and docs.
- [X] I've picked the right materialization for the affected models.

# Other

- [X] Check if a full-refresh is required after this PR is merged. **Need to create the seed manually**

Related work items: #26618

models/intermediate/xero/schema.yml

@@ -271,7 +271,17 @@ models:
         description: |
           The default macro-aggregation for Invoiced KPIs.
 
-      - name: accounting_financial_aggregation
+      - name: accounting_financial_l1_aggregation
         data_type: character varying
         description: |
-          The default macro-aggregation for Financial reporting.
+          The Level 1 aggregation for Financial reporting.
+
+      - name: accounting_financial_l2_aggregation
+        data_type: character varying
+        description: |
+          The Level 2 aggregation for Financial reporting.
+
+      - name: accounting_financial_l3_aggregation
+        data_type: character varying
+        description: |
+          The Level 3 aggregation for Financial reporting.