Merged PR 2317: Exposing first_day_month for business kpis

This PR exposes the field first_day_month in the business KPIs, for the Global view. It's just to be able to properly display graphs, since it's quite confusing doing it so by last_day_month (see screenshot)![image.png](https://guardhog.visualstudio.com/4148d95f-4b6d-4205-bcff-e9c8e0d2ca65/_apis/git/repositories/54ac356f-aad7-46d2-b62c-e8c5b3bb8ebf/pullRequests/2317/attachments/image.png)

Related work items: #18580

models/intermediate/cross/int_mtd_aggregated_metrics.sql

@@ -243,6 +243,7 @@ with
         day,
         is_end_of_month,
         is_current_month,
+        first_day_month,
         date,
         previous_year_date,
         {{ metric.order_by }} as order_by,

models/intermediate/cross/int_mtd_vs_previous_year_metrics.sql

@@ -32,6 +32,7 @@ with
             d.day,
             d.is_end_of_month,
             d.is_current_month,
+            d.first_day_month,
             d.date,
 
             -- BOOKINGS --
@@ -146,6 +147,7 @@ select
     current.day,
     current.is_end_of_month,
     current.is_current_month,
+    current.first_day_month,
     current.date,
     previous_year.date as previous_year_date,
 

models/intermediate/cross/schema.yml

@@ -235,6 +235,14 @@ models:
         tests:
           - not_null
 
+      - name: first_day_month
+        data_type: date
+        description: |
+          first day of the month correspoding to the date field. 
+          It comes from int_dates_mtd logic.
+        tests:
+          - not_null
+
       - name: date
         data_type: date
         description: |