Workhorse: Disable S3 Content-MD5 header in FIPS mode

As @igor.drozdov mentioned in https://gitlab.com/gitlab-org/gitlab/-/issues/352272#note_909887510, we should set S3DisableContentMD5Validation to true in Workhorse when FIPS mode is enabled (fips.Check() from LabKit is true). MD5 cannot be used in a FIPS-compliant system, and this flag causes X-Amz-Content-Sha256 to be used instead.