Index UI should alert when the index build is below certain threshold

This is related to MB-50396

 Index memory quota is too small for it be able to create the index (index_red:adv_type_CMAPALTA_cajero - "items_count":227143138)

In this case, the index build process was still running, albeit very slow.

We should add an alert to the Index UI to notify the user when the Index memory resident < 5% during the build (i.e. mutations pending as in the above MB)