fix(coderd/database): exclude canceled jobs in queue position (#15835)

When calculating the queue position in
`GetProvisionerJobsByIDsWithQueuePosition` we only counted jobs with
`started_at = NULL`. This is misleading, as it allows canceling or
canceled jobs to take up rows in the computed queue position, giving an
impression that the queue is larger than it really is.

This modifies the query to also exclude jobs with a null `canceled_at`,
`completed_at`, or `error` field for the purposes of calculating the
queue position, and also adds a test to validate this behaviour.

(Note: due to the behaviour of `dbgen.ProvisionerJob` with `dbmem` I had
to use other proxy methods to validate the corresponding dbmem
implementation.)

---------

Co-authored-by: Mathias Fredriksson <mafredri@gmail.com>

coderd/database/queries.sql.go

@@ -5865,23 +5865,29 @@ func (q *sqlQuerier) GetProvisionerJobsByIDs(ctx context.Context, ids []uuid.UUI
 }
 
 const getProvisionerJobsByIDsWithQueuePosition = `-- name: GetProvisionerJobsByIDsWithQueuePosition :many
-WITH unstarted_jobs AS (
+WITH pending_jobs AS (
     SELECT
         id, created_at
     FROM
         provisioner_jobs
     WHERE
         started_at IS NULL
+    AND
+        canceled_at IS NULL
+    AND
+        completed_at IS NULL
+    AND
+        error IS NULL
 ),
 queue_position AS (
     SELECT
         id,
         ROW_NUMBER() OVER (ORDER BY created_at ASC) AS queue_position
     FROM
-        unstarted_jobs
+        pending_jobs
 ),
 queue_size AS (
-	SELECT COUNT(*) as count FROM unstarted_jobs
+	SELECT COUNT(*) AS count FROM pending_jobs
 )
 SELECT
 	pj.id, pj.created_at, pj.updated_at, pj.started_at, pj.canceled_at, pj.completed_at, pj.error, pj.organization_id, pj.initiator_id, pj.provisioner, pj.storage_method, pj.type, pj.input, pj.worker_id, pj.file_id, pj.tags, pj.error_code, pj.trace_metadata, pj.job_status,