PUT admission since #4928 rejected any request whose Content-Encoding declares
aws-chunked but lacks x-amz-decoded-content-length with 400 UnexpectedContent.
Whether the body is actually chunk-framed is signalled by a STREAMING-*
x-amz-content-sha256, not by the declared encoding: the s3s auth layer only
de-frames streaming payloads and already requires the decoded length for them,
so a declared-only aws-chunked request (issue #1857 clients) carries an
unframed body whose wire Content-Length is the authoritative object size.
Admit it against that length; keep failing closed for genuinely framed bodies
without a decoded length, and use the decoded length for streaming payloads
even when Content-Encoding is absent.
Refs: https://github.com/rustfs/backlog/issues/1336
cxymds