Merged PR 2824: Propagates Billing Country and Deal Name into int_dates_by_deal

# Description

Changes:
* Adding `main_deal_name` and `main_billing_country_iso_3_per_deal` in `int_dates_by_deal` model.
* Documents the 2 new fields. Also, ensures `main_deal_name` is not null
* Removes `id_deal not null` condition since it's enforced on the inner join with `int_core__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

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

Related work items: #18911, #19083

models/intermediate/cross/schema.yml

@@ -303,6 +303,19 @@ models:
         tests:
           - not_null
 
+      - name: main_deal_name
+        data_type: string
+        description: |
+          Main name for this ID deal.
+        tests:
+          - not_null
+
+      - name: main_billing_country_iso_3_per_deal
+        data_type: string
+        description: |
+          ISO 3166-1 alpha-3 main country code in which the Deal is billed.
+          In some cases it's null.
+
   - name: int_mtd_aggregated_metrics
     description: |
       The `int_mtd_aggregated_metrics` model aggregates multiple metrics on a year, month, and day basis.