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 for the S3 client 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.

This is similar to gitlab#361285 (closed).