Move env var config loading to be within the config package. am: 2f504db7 am: 4d5f00fe

Original change: https://googleplex-android-review.googlesource.com/c/platform/build/soong/+/18971604



Change-Id: Ia6f255e1d244af8301831133095dc5c14b8d1ccd
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>