This commit adds basic support for SSE-C / SSE-C copy.
This includes functions for determining whether SSE-C
is requested by the S3 client and functions for parsing
such HTTP headers.
All S3 SSE-C parsing errors are exported such that callers
can pattern-match to forward the correct error to S3
clients.
Further the SSE-C related internal metadata entry-keys
are added by this commit.
758a80e39b