PushToBuildStorage should allow divergent blob and local storage paths

- [ ] This issue is blocking
- [ ] This issue is causing unreasonable pain

When PushToLocalStorage is true (V4 publishing or when set explicitly), artifacts are copied to a local staging location before AzDO uploads them. This local staging location is defined by the relative blob path that the artifact will eventually end up at in blob storage. Publishing then finds the source artifact in the build based on the artifact name and this relative path.

It would be ideal if the relative local staging location could be different than the relative blob path. This would allow some flexibility in cases where teams or existing tools look for artifacts at old locations.

Start by tracing PushToBuildStorage and PushToLocalStorage through V4 publishing and the artifact lookup path. Confirm how the relative blob path currently determines the local staging location. Done means a local staging path can differ from the blob path while publishing still finds and uploads the intended artifact.

Written by the indexing model from the issue text.