refactor cmd/crypto code for SSE handling and parsing (#11045)

This commit refactors the code in `cmd/crypto`
and separates SSE-S3, SSE-C and SSE-KMS.

This commit should not cause any behavior change
except for:
  - `IsRequested(http.Header)`

which now returns the requested type {SSE-C, SSE-S3,
SSE-KMS} and does not consider SSE-C copy headers.

However, SSE-C copy headers alone are anyway not valid.

cmd/disk-cache-backend.go

@@ -962,7 +962,7 @@ func (c *diskCache) Get(ctx context.Context, bucket, object string, rs *HTTPRang
 	}
 	if globalCacheKMS != nil {
 		// clean up internal SSE cache metadata
-		delete(gr.ObjInfo.UserDefined, crypto.SSEHeader)
+		delete(gr.ObjInfo.UserDefined, xhttp.AmzServerSideEncryption)
 	}
 	if !rngInfo.Empty() {
 		// overlay Size with actual object size and not the range size