Merged PR 3766: First version of ab_test_tracking_guest_journey

# Description

A very simple, clean table to get the records needed for A/B test tracking on GJ side.

The table already removes weird cases that are somehow usual within A/B test configurations, to ensure that the monitoring is as clean (and less biased) as possible.

# 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: #25145

models/intermediate/core/int_core__ab_test_tracking_guest_journey.sql

@@ -0,0 +1,46 @@
+{{
+    config(
+        materialized="table", unique_key=["id_verification_request", "ab_test_name"]
+    )
+}}
+with
+    stg_core__verification_request_feature_flag as (
+        select * from {{ ref("stg_core__verification_request_feature_flag") }}
+    ),
+    clean_ab_test_data as (
+        select
+            id_verification_request,
+            feature_flag_name as ab_test_name,
+            feature_flag_variation as variation,
+            min(created_at_utc) as first_appearance_at_utc,
+            max(created_at_utc) as last_appearance_at_utc
+        from stg_core__verification_request_feature_flag
+        where
+            feature_flag_variation is not null
+            and feature_flag_variation <> ''
+            and is_feature_flag_enabled = true
+        group by 1, 2, 3
+    ),
+    variations_per_request_and_test as (
+        select
+            id_verification_request,
+            ab_test_name,
+            count(distinct variation) as number_of_different_variations
+        from clean_ab_test_data
+        group by 1, 2
+    )
+select
+    c.id_verification_request,
+    c.ab_test_name,
+    c.variation,
+    c.first_appearance_at_utc,
+    c.last_appearance_at_utc
+from clean_ab_test_data c
+inner join
+    variations_per_request_and_test v
+    on c.id_verification_request = v.id_verification_request
+    and c.ab_test_name = v.ab_test_name
+-- The following is to ensure that if for whatever reason a given verification request
+-- has more than one variation in the same A/B test, this data is removed from the
+-- A/B test tracking
+where v.number_of_different_variations = 1

models/intermediate/core/schema.yml

@@ -4271,3 +4271,65 @@ models:
           Date of when this Protection Plan Billing Item record was last updated.
         tests:
           - not_null
+
+  - name: int_core__ab_test_tracking_guest_journey
+    description: |
+      Provides the A/B test tracking of a given Verification Request, aka Guest Journey.
+      For those Guest Journeys that are subject to A/B testing through Feature Flagging, 
+      this table will provide the id of the verification request, the A/B test name in 
+      which is in and the variation, as well as additional metadata. 
+
+      This table already contains cleaning of multi-variant guest journeys and disablement 
+      of the feature flag (A/B test) itself, so should be quite ready to use.
+
+    tests:
+      - dbt_utils.unique_combination_of_columns:
+          combination_of_columns:
+            - id_verification_request
+            - ab_test_name
+
+    columns:
+      - name: id_verification_request
+        data_type: integer
+        description: |
+          Identifier of the Verification Request. Acts as foreign key to the Verification Request table.
+          It can be duplicated across different Feature Flags - meaning the same verification request 
+          can be part of none, one, or several A/B tests. 
+          In this table, a Verification Request or Guest Journey can only appear once per A/B test.
+          Cannot be null.
+        tests:
+          - not_null
+
+      - name: ab_test_name
+        data_type: string
+        description: |
+          Name of the Guest Journey A/B test. It corresponds to the Feature Flag Name in the 
+          backend. Cannot be null.
+        tests:
+          - not_null
+
+      - name: variation
+        data_type: string
+        description: |
+          Identifier of the variation a given Verification Request is in, within a
+          given Guest Journey A/B test. Cannot be null.
+        tests:
+          - not_null
+
+      - name: first_appearance_at_utc
+        data_type: timestamp
+        description: |
+          Timestamp of the first Verification Request Feature Flag record created 
+          with the same verification request and A/B test name. Mostly for information 
+          purposes. Cannot be null.
+        tests:
+          - not_null
+
+      - name: last_appearance_at_utc
+        data_type: timestamp
+        description: |
+          Timestamp of the last Verification Request Feature Flag record created 
+          with the same verification request and A/B test name. Mostly for information 
+          purposes. Cannot be null.
+        tests:
+          - not_null