Merged PR 4759: Adds Booking Fee per Billable Booking

# Description

Changes:
* Creates Booking Fees in YTD/MTD
* Creates Booking Fees per Billable Booking in YTD/MTD. This is exposed forward.
* Removes code for Onboarding MRR in YTD/MTD.

Additional fixes:
* Small mistake - Revenue Churn is now considered as NEGATIVE

# 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: #28560

models/intermediate/cross/schema.yml

@@ -2135,10 +2135,15 @@ models:
         description: |
           Total revenue churn rate for the current month MTD.
 
-      - name: current_month_mtd_onboarding_mrr
+      - name: current_month_mtd_booking_net_fees_in_gbp
         data_type: numeric
         description: |
-          Total expected Onboarding MRR for the current month MTD.
+          Total Booking net fees in gbp for the current month MTD.
+
+      - name: current_month_mtd_booking_net_fees_per_billable_booking
+        data_type: numeric
+        description: |
+          Total Booking net fees per billable booking for the current month MTD.
 
       - name: previous_year_mtd_billable_bookings
         data_type: integer
@@ -2250,11 +2255,17 @@ models:
           Total revenue churn rate for the previous year 
           (12 months ago) MTD.
 
-      - name: previous_year_mtd_onboarding_mrr
+      - name: previous_year_mtd_booking_net_fees_in_gbp
         data_type: numeric
         description: |
-          Total expected Onboarding MRR for the previous year 
-          (12 months ago) MTD.
+          Total Booking net fees in gbp for the previous 
+          year (12 months ago) MTD.
+
+      - name: previous_year_mtd_booking_net_fees_per_billable_booking
+        data_type: numeric
+        description: |
+          Total Booking net fees per billable booking for the 
+          previous year (12 months ago) MTD.
 
       - name: current_ytd_billable_bookings
         data_type: integer
@@ -2364,10 +2375,16 @@ models:
         description: |
           Total revenue churn rate for the current financial year YTD.
 
-      - name: current_ytd_onboarding_mrr
+      - name: current_ytd_booking_net_fees_in_gbp
         data_type: numeric
         description: |
-          Total expected Onboarding MRR for the current financial year YTD.
+          Total booking net fees in gbp for the current financial year YTD.
+
+      - name: current_ytd_booking_net_fees_per_billable_booking
+        data_type: numeric
+        description: |
+          Total booking net fees per billable booking for the 
+          current financial year YTD.
 
       - name: previous_ytd_billable_bookings
         data_type: integer
@@ -2478,11 +2495,16 @@ models:
           Total revenue churn rate for the previous 
           financial year YTD.
 
-      - name: previous_ytd_onboarding_mrr
+      - name: previous_ytd_booking_net_fees_in_gbp
         data_type: numeric
         description: |
-          Total expected Onboarding MRR for the previous 
-          financial year YTD.
+          Total booking net fees in gbp for the previous financial year YTD.
+
+      - name: previous_ytd_booking_net_fees_per_billable_booking
+        data_type: numeric
+        description: |
+          Total booking net fees per billable booking for the 
+          previous financial year YTD.
 
       - name: previous_month_eom_billable_bookings
         data_type: integer
@@ -2600,11 +2622,17 @@ models:
           Total revenue churn rate for the previous month, 
           at the end of the month.
 
-      - name: previous_month_eom_onboarding_mrr
+      - name: previous_month_eom_booking_net_fees_in_gbp
         data_type: numeric
         description: |
-          Total expected Onboarding MRR for the previous month, 
-          at the end of the month.
+          Total booking net fees in gbp for the previous 
+          month at the end of the month.
+
+      - name: previous_month_eom_booking_net_fees_per_billable_booking
+        data_type: numeric
+        description: |
+          Total booking net fees per billable booking for the 
+          previous month at the end of the month.
 
   - name: int_ytd_mtd_aggregated_main_metrics_overview
     description: |