Merged PR 2676: Propagates Billing Country information

# Description

Propagates Billing Country information in unified_user and user_host intermediate models. This is a necessary step towards providing KPIs segmented by Billing Country.

# 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: #19082

models/intermediate/core/int_core__unified_user.sql

@@ -1,12 +1,16 @@
 with
     stg_core__user as (select * from {{ ref("stg_core__user") }}),
     stg_core__superhog_user as (select * from {{ ref("stg_core__superhog_user") }}),
-    stg_core__currency as (select * from {{ ref("stg_core__currency") }})
+    stg_core__currency as (select * from {{ ref("stg_core__currency") }}),
+    stg_core__country as (select * from {{ ref("stg_core__country") }})
 select
     u.id_user,
     u.id_account_type,
     u.id_billing_country,
-    c.iso4217_code as account_currency_iso4217,
+    co.country_name as billing_country_name,
+    co.iso_2 as billing_country_iso_2,
+    co.iso_3 as billing_country_iso_3,
+    cu.iso4217_code as account_currency_iso4217,
     u.user_code,
     u.first_name,
     u.last_name,
@@ -42,4 +46,5 @@ select
     su.id_user_verification_status
 from stg_core__user as u
 inner join stg_core__superhog_user as su on u.id_user = su.id_superhoguser
-left join stg_core__currency c on u.id_account_currency = c.id_currency
+left join stg_core__currency cu on u.id_account_currency = cu.id_currency
+left join stg_core__country co on u.id_billing_country = co.id_country

models/intermediate/core/int_core__user_host.sql

@@ -31,6 +31,9 @@ select
     uu.id_user as id_user_host,
     uu.id_account_type,
     uu.id_billing_country,
+    uu.billing_country_name,
+    uu.billing_country_iso_2,
+    uu.billing_country_iso_3,
     uu.account_currency_iso4217,
     uu.user_code,
     uu.first_name,

models/intermediate/core/schema.yaml

@@ -2111,6 +2111,21 @@ models:
         description: |
           ID of the country in which the Host is billed. 
           In some cases it's null.
+      - name: billing_country_name
+        data_type: string
+        description: |
+          Name of the country in which the Host is billed.
+          In some cases it's null.
+      - name: billing_country_iso_2
+        data_type: string
+        description: |
+          ISO 3166-1 alpha-2 country code in which the Host is billed.
+          In some cases it's null.
+      - name: billing_country_iso_3
+        data_type: string
+        description: |
+          ISO 3166-1 alpha-3 country code in which the Host is billed.
+          In some cases it's null.     
       - name: account_currency_iso4217
         data_type: string
         description: |