This commit adds basic SSE-KMS support.
Now, a client can specify the SSE-KMS headers
(algorithm, optional key-id, optional context)
such that the object gets encrypted using the
SSE-KMS method. Further, auto-encryption now
defaults to SSE-KMS.
This commit does not try to do any refactoring
and instead tries to implement SSE-KMS as a minimal
change to the code base. However, refactoring the entire
crypto-related code is planned - but needs a separate
effort.
Signed-off-by: Andreas Auernhammer <aead@mail.de>