The RGW support server side encryption with help of s3 protocol, till
now the `sse:kms` was support in which keys will be provided by the user
and but it will be saved in external management service like vault. Now
the support for `sse:s3` is added so the entire encryption key
management is performed by RGW itsels.
Signed-off-by: Jiffin Tony Thottan <thottanjiffin@gmail.com>