avg_page_load_time import not supported

[diosmosis]

It can be added, possibly, there's a metric ga:avgPageLoadTime which can be used, but it's non-trivial to use it, since Matomo calculates avg_page_load_time by adding all the other averaged page performance metrics together.

We'd need to somehow import every one of the metrics that are actually stored as records in PagePerformance.