Move `pesummary.core.plots.interpolate` to utils module
The purpose of this MR is to move the pesummary.core.plots.interpolate
module to the pesummary.utils
directory so it is in the same location as the KDE
module.
The purpose of this MR is to move the pesummary.core.plots.interpolate
module to the pesummary.utils
directory so it is in the same location as the KDE
module.