fix: Only update workspace LastUsed when the connection payload has changed (#4115)

This was causing every workspace to update last used to time.Now() when
coderd was restarted!

coderd/database/queries.sql.go

@@ -24,6 +24,25 @@ func (q *sqlQuerier) DeleteOldAgentStats(ctx context.Context) error {
 	return err
 }
 
+const getLatestAgentStat = `-- name: GetLatestAgentStat :one
+SELECT id, created_at, user_id, agent_id, workspace_id, template_id, payload FROM agent_stats WHERE agent_id = $1 ORDER BY created_at DESC LIMIT 1
+`
+
+func (q *sqlQuerier) GetLatestAgentStat(ctx context.Context, agentID uuid.UUID) (AgentStat, error) {
+	row := q.db.QueryRowContext(ctx, getLatestAgentStat, agentID)
+	var i AgentStat
+	err := row.Scan(
+		&i.ID,
+		&i.CreatedAt,
+		&i.UserID,
+		&i.AgentID,
+		&i.WorkspaceID,
+		&i.TemplateID,
+		&i.Payload,
+	)
+	return i, err
+}
+
 const getTemplateDAUs = `-- name: GetTemplateDAUs :many
 select
 	(created_at at TIME ZONE 'UTC')::date as date,