Support skipping of ETag verification for object storage

Some S3 providers and transfer modes in Amazon S3 do not have ETags that match the MD5 sum of the file. For these providers, we should provide a way to skip this ETag verification until gitlab-workhorse#222 (closed) is implemented.

This change sends the flag to Worhorse if the skip_etag_verify config option is set. This flag will be used by gitlab-workhorse!427 (closed)

Relates to:

• gitlab-workhorse#210 (closed)
• gitlab-org/charts/gitlab#1564 (closed)