Merged PR 5429: Rework Booking Source in int_core__bookings

# Description

This PR creates a proper Booking Source in `int_core__bookings` table. This mostly refers to ensure that whenever we do data requests tickets on this regards we have a proper logic in place (as last time we had issues because of this). Logic follows Gus recommendation on applying:

```
case
  when upper(coalesce(bsrc.booking_source, 'UNKNOWN')) = 'UNKNOWN'
  then b.raw_booking_source
  else bsrc.booking_source
end
```

where b. is Booking table and bsrc. is Booking Source table.

Things to note:
* A new `stg_core__booking_source` table is created, full-refreshed from the backend (less than 10 records)
* I added a unique test for `stg_core__booking` that was not in there. I don't document the rest of the model though.
* I remove the previous `id_booking_source` as it wasn't used and the logic in place should be far more accurate.
* I do NOT remove the existing `verification_request_booking_source`. I don't remember what's this but I see this is in use specially on Guest Insights (CSAT) and the legacy Truvi reporting (Bookings, PMS, etc.). Not the scope of this ticket to change it.
* I don't do further propagation, but potentially, this could be extended to New Dash Booking Summary as this source is being shown in the dashboard itself.

# 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: #30415

models/staging/core/_core_sources.yml

@@ -283,6 +283,8 @@ sources:
         identifier: VerificationRequestGuestProductToPayment
       - name: UserProductBundleToGuestProduct
         identifier: UserProductBundleToGuestProduct
+      - name: BookingSource
+        identifier: BookingSource
 
   - name: guest_product
     schema: sync_guest_product

models/staging/core/schema.yml

@@ -114,6 +114,24 @@ models:
           - unique
           - not_null
 
+  - name: stg_core__booking
+    columns:
+      - name: id_booking
+        data_tests:
+          - unique
+          - not_null
+
+  - name: stg_core__booking_source
+    columns:
+      - name: id_booking_source
+        data_tests:
+          - unique
+          - not_null
+      - name: booking_source
+        data_tests:
+          - unique
+          - not_null
+
   - name: stg_core__accommodation_to_user
     columns:
       - name: id_accommodation_to_user

models/staging/core/stg_core__booking.sql

@@ -21,6 +21,7 @@ with
             {{ adapter.quote("IntegrationId") }} as id_integration,
             {{ adapter.quote("AccommodationId") }} as id_accommodation,
             {{ adapter.quote("BookingSourceId") }} as id_booking_source,
+            {{ adapter.quote("RawBookingSource") }} as raw_booking_source,
             {{ adapter.quote("VerificationRequestId") }} as id_verification_request,
             {{ adapter.quote("BookingStateId") }} as id_booking_state,
             {{ adapter.quote("CheckIn") }} as check_in_at_utc,

models/staging/core/stg_core__booking_source.sql

@@ -0,0 +1,12 @@
+with
+    raw_booking_source as (select * from {{ source("core", "BookingSource") }}),
+    stg_core__booking_source as (
+        select
+            {{ adapter.quote("Id") }} as id_booking_source,
+            upper({{ adapter.quote("FullName") }}) as booking_source,
+            {{ adapter.quote("_airbyte_extracted_at") }} as dwh_extracted_at_utc
+
+        from raw_booking_source
+    )
+select *
+from stg_core__booking_source