chore: replace GetManagedAgentCount query with aggregate table (#19636)

- Removes GetManagedAgentCount query
- Adds new table `usage_events_daily` which stores aggregated usage
events by the type and UTC day
- Adds trigger to update the values in this table when a new row is
inserted into `usage_events`
- Adds a migration that adds `usage_events_daily` rows for existing data
in `usage_events`
- Adds tests for the trigger
- Adds tests for the backfill query in the migration

Since the `usage_events` table is unreleased currently, this migration
will do nothing on real deployments and will only affect preview
deployments such as dogfood.

Closes https://github.com/coder/internal/issues/943

coderd/database/queries/licenses.sql

@@ -35,28 +35,3 @@ DELETE
 FROM licenses
 WHERE id = $1
 RETURNING id;
-
--- name: GetManagedAgentCount :one
--- This isn't strictly a license query, but it's related to license enforcement.
-SELECT
-	COUNT(DISTINCT wb.id) AS count
-FROM
-	workspace_builds AS wb
-JOIN
-	provisioner_jobs AS pj
-ON
-	wb.job_id = pj.id
-WHERE
-	wb.transition = 'start'::workspace_transition
-	AND wb.has_ai_task = true
-	-- Only count jobs that are pending, running or succeeded. Other statuses
-	-- like cancel(ed|ing), failed or unknown are not considered as managed
-	-- agent usage. These workspace builds are typically unusable anyway.
-	AND pj.job_status IN (
-		'pending'::provisioner_job_status,
-		'running'::provisioner_job_status,
-		'succeeded'::provisioner_job_status
-	)
-	-- Jobs are counted at the time they are created, not when they are
-	-- completed, as pending jobs haven't completed yet.
-	AND wb.created_at BETWEEN @start_time::timestamptz AND @end_time::timestamptz;