amari.kpi: Add support for DRB.UEActive measurement
Expand upon the new data models introduced in !9 (merged) by teaching the amari.kpi
driver to populate the DRB.UEActive
Measurement field.
Mirroring the kpi
module, some additional infrastructure is added to the driver in order to support statistical profiles, even though it is only the necessary per-cell measurement extraction utilities for now. The rest can be comfortably added as they will be needed in the future.