Can't create a repository on a S3 bucket with object lock and default retention

[michaelcourcy]

Hi

I can't create a repository on a bucket with object lock enabled and default retention.

michael-3-locked is a bucket where I enable object lock and set a default retention period of 1 day.

kopia repository create s3 \
        --bucket=michael-3-locked \
        --access-key=AKIAWWWWWWW \
        --secret-access-key=YYYYYYXXXXXXXX

Enter password to create new repository: 
Re-enter password for verification: 
Initializing repository with:
  block hash:          BLAKE2B-256-128
  encryption:          AES256-GCM-HMAC-SHA256
  splitter:            DYNAMIC-4M-BUZHASH
kopia: error: cannot initialize repository: unable to write format blob: unable to write format blob: Content-MD5 HTTP header is required for Put Object requests with Object Lock parameters, try --help

It seems that when you need to put object with lock parameters you need this extra Content-MD5 header.

[julio-lopez]

Also somewhat related to #762