object_store: Uploading empty file to S3 results in "411 Length Required"

[Turbo87]

Describe the bug

When using the S3 implementation of object_store a put() call with an empty content fails on the server side with a "411 Length Required" error:

Generic S3 error: response error "<?xml version="1.0" encoding="UTF-8"?>
<Error><Code>MissingContentLength</Code><Message>You must provide the Content-Length HTTP header.</Message></Error>", after 0 retries: HTTP status client error (411 Length Required) for url (https://s3.us-west-2.amazonaws.com/...)

To Reproduce

s3_store.put(&"foo".into(), Bytes::new()).await.unwrap()

Expected behavior

The call succeeds and uploads an empty file to S3.

Additional context

• Zero length README.md files cause worker errors rust-lang/crates.io#6793

[tustvold]

label_issue.py automatically added labels {'object-store'} from #4518