Merged PR 4124: Adds dedicated start date for KPIs

# Description

This is a extremely simple but rather important PR.
It just sets the cutoff for KPIs reporting to April 2022. This affects 1) Main KPIs, 2) Guest KPIs and 3) Account Managers report

Motivation behind this is to have accurate data. Early 2022 might still be shitty, but at least we have a source of truth to compare against (on revenue side, finance P&L)

I set a dedicated variable because currency rates is reading from the same start date, and I intend only to modify KPIs cutoff.

# Checklist

- [X] The edited models and dependants run properly with production data.
- [NA] The edited models are sufficiently documented.
- [NA] The edited models contain PK tests, and I've ran and passed them.
- [NA] I have checked for DRY opportunities with other models and docs.
- [NA] I've picked the right materialization for the affected models.

# Other

- [ ] Check if a full-refresh is required after this PR is merged. **I need to manually run a full-refresh on daily listing segmentation that is incremental**

Adds dedicated start date for KPIs

Related work items: #26712

models/intermediate/kpis/int_kpis__dimension_date_product_guest.sql

@@ -15,4 +15,4 @@ select
     ud.main_billing_country_iso_3_per_deal
 from {{ ref("int_dates") }} as d
 cross join unique_dimensions as ud
-where d.date_day >= {{ var("start_date") }}
+where d.date_day >= {{ var("kpis_start_date") }}

models/intermediate/kpis/int_kpis__dimension_dates.sql

@@ -2,7 +2,9 @@
 
 with
     int_dates as (
-        select * from {{ ref("int_dates") }} where date_day >= {{ var("start_date") }}
+        select *
+        from {{ ref("int_dates") }}
+        where date_day >= {{ var("kpis_start_date") }}
     ),
     raw_dates as (
         select