feature: ZENKO-1420 return locations from backbeat PUT routes
feature: ZENKO-1420 return locations from backbeat PUT routes

Return the locations array in the API of putObject and completeMPU
multiple backend routes, so that transition policies can use it to
update metadata with the new location as-is.

scality/S3,scality/S3,scality/S3,scality/S3,scality/S3,scality/S3,scality/S3,scality/S3