S3 publishing encodes regions in the URLs

The NFT metadata contains links like:
```
https://s3.us-east-1.amazonaws.com/foo-project/...
```

rather than a region-agnostic form, like:
```
https://foo-project.s3.amazonaws.com/...
```

It would be slightly preferable to use region-agnositic asset URLs, in case the assets are migrated between regions.