Avoid configuration drift between ci-xxx and packages/vfx dockerfiles

The Dockerfiles used to build the ci-xxx images are autogenerated from `ci-xxx/image.yaml` and are used to build the ci-xxx CI build images for the ASWF + USD projects.

But when building those projects to include as dependencies in higher level ci-xxx images or for the all-inclusive ci-vfxall project, we use the pre-baked Dockerfiles in `packages/vfx1` and `packages/vfx2`

This can result in drift between these build environments, as well as violating the DRY principle.

We should figure out a way to have a single, authoritative definition for the build environment of a package that gets used in both cases.

Compare the generated ci-xxx Dockerfiles from ci-xxx/image.yaml with the pre-baked Dockerfiles in packages/vfx1 and packages/vfx2. Trace how each is used for dependency and all-inclusive ci-vfxall images, then determine a single authoritative build definition that serves both paths. Done means the two environments no longer drift and the duplicated definitions are removed or generated consistently.

Written by the indexing model from the issue text.