Merged PR 4425: Reworks Billable Bookings metrics

# Description

Changes:
* On Est. Billable Bookings, keeps previous logic for Old Dash while assuming the first billable service for New Dash
* Adds a Billable Check Out Bookings in Check Out bookings, as defined in the requirements.

# 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: #27619

models/intermediate/cross/int_mtd_aggregated_metrics.sql

@@ -53,6 +53,15 @@
         "number_format": "integer",
         "increment_sign_format": "positive",
     },
+    {
+        "order_by": 8,
+        "metric": "Billable Check Out Bookings",
+        "value": "billable_check_out_bookings",
+        "previous_year_value": "previous_year_billable_check_out_bookings",
+        "relative_increment": "relative_increment_billable_check_out_bookings",
+        "number_format": "integer",
+        "increment_sign_format": "positive",
+    },
     {
         "order_by": 9,
         "metric": "Est. Billable Bookings",