At the end of CalibrateTask, we'll want to compute the PSF and aperture fluxes of the PSF stars, and send those to the PSF model to be stored and interpolated (using the featured added via DM-434).

We'll also need to run any other flux measurement algorithms that need to be tied to the PSF fluxes on these same stars; because these can be somewhat slow, we probably want to limit these measurements to only the PSF stars, rather than requiring all these algorithms to be run as part of calibrate.measurement. The relationships between these fluxes and the PSF fluxes will be additional fields to be added to and interpolated by the PSF.

The HSC implementation of this work (as well as that of DM-436) was done on issue HSC-191:
https://hsc-jira.astro.princeton.edu/jira/browse/HSC-191
There were changes to many packages, but the relevant ones for LSST are:
https://github.com/HyperSuprime-Cam/afw/commit/057fb3c0581c512d5664f1883a72da950c9eae9d
https://github.com/HyperSuprime-Cam/meas_algorithms/compare/HSC-3.0.0...u/jbosch/DM-191
https://github.com/HyperSuprime-Cam/pipe_tasks/compare/4c3a53e7238cbe9...u/jbosch/DM-191