The goal of this RFC is to add a new package to `lsst_distrib` which will be a library used in the creation of ci_* packages. The proposed name for this package is `ci_builder`.

This is meant to solve the issues that arise from using `scons` to orchestrate running ci jobs, as well as some other pain points developers have run into.

Currently the plan is to use this system to implement a new `ci_imsim` package and overhaul `ci_hsc_gen3`, but it is expected to be generally useful for many other ci tools, and potentially other tools in the future.