Merged PR 4107: First version of accounting aggregations

# Description

Creates a seed to define how to aggregate the different revenue/cost sources, at account code level.

This is propagated to the sales denom mart in intermediate.

This is not complete, but should be a good starting point and it enables moving forward with a couple of tickets regarding KPIs revenue refactor and further Finance reporting, by just keeping a single source of truth. It's mostly focusing on the Don't Repeat Yourself

# 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

- [ ] Check if a full-refresh is required after this PR is merged.

First version of accounting aggregations - not complete

Related work items: #26618

models/intermediate/xero/schema.yml

@@ -259,3 +259,19 @@ models:
       - name: contact_name
         data_type: character varying
         description: ""
+
+      - name: accounting_root_aggregation
+        data_type: character varying
+        description: |
+          The root aggregation per account code. This is the main
+          aggregation that is used to retrieve low-level data.
+
+      - name: accounting_kpis_aggregation
+        data_type: character varying
+        description: |
+          The default macro-aggregation for Invoiced KPIs.
+
+      - name: accounting_financial_aggregation
+        data_type: character varying
+        description: |
+          The default macro-aggregation for Financial reporting.