Merged PR 4572: Applies logic to modify the invoicing cycle date depending on the issuing source

# Description

Hyperline invoices/credit notes have an issuing date that corresponds to the moment in which these are actually created.

This is an issue since it means that an invoice or credit note posted today, 4th March 2025, that is supposed to be related to February 2025 invoicing cycle, will have:

* If the document is posted in Hyperline, an issuing date on the March 2025
* If the document is NOT posted in Hyperline, an issuing date on February 2025

This PR just creates a field that handles the logic effectively, to be used further in other reports/kpis purposes.

# 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.

Related work items: #28158

models/intermediate/xero/schema.yml

@@ -204,6 +204,14 @@ models:
         data_type: date
         description: ""
 
+      - name: document_is_effective_at_end_of_month_utc
+        data_type: date
+        description: |
+          The last day of the month when the document is effective. 
+          This is used to align the document with the correct invoicing cycle period.
+          For documents posted in Hyperline, this represents the last day of the previous 
+          month to the issuing date. For documents not posted in Hyperline, this is the 
+          last day of the month when the document was issued.
       - name: document_type
         data_type: character varying
         description: ""