Use S3Batch for object tag removal

During the dandiset unembargo process, we remove the `embargoed` tag from all objects associated with that dandiset. This is often times many objects, and can be difficult to achieve while balancing speed and reliability (see https://github.com/dandi/dandi-archive/pull/2549).

[S3Batch](https://docs.aws.amazon.com/AmazonS3/latest/userguide/batch-ops.html) can instead be used to perform these operations, and should be more efficient, with less room for error.

Start by reviewing the unembargo workflow and pull request #2549, then read the AWS S3Batch documentation linked in the issue. The work is complete when removing the embargoed tag for a dandiset uses S3 Batch Operations reliably for large object sets, with the relevant behavior verified by the project’s existing checks.

Written by the indexing model from the issue text.