Merged PR 2730: Exposing Billable Bookings metric for KPIs

# Description

Exposes Billable Bookings metric for KPIs, both in the "global+dimension" view and in the "deal" view.

Metrics have already been created for a while. Exposing them now after the changes carried out in the model `int_core__booking_charge_events`. Based on the current quality of the data, I opted for "Est. Billable Bookings" to account for the fact that this is an estimation. If you don't feel comfortable with it, let's remove the "Est. ".

# 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: #18111

models/intermediate/cross/int_mtd_aggregated_metrics.sql

@@ -28,6 +28,15 @@
     },
     {
         "order_by": 4,
+        "metric": "Est. Billable Bookings",
+        "value": "billable_bookings",
+        "previous_year_value": "previous_year_billable_bookings",
+        "relative_increment": "relative_increment_billable_bookings",
+        "number_format": "integer",
+        "increment_sign_format": "positive",
+    },
+    {
+        "order_by": 10,
         "metric": "Guest Journey Created",
         "value": "created_guest_journeys",
         "previous_year_value": "previous_year_created_guest_journeys",