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/object-api-utils_test.go

@@ -347,7 +347,7 @@ func TestIsCompressed(t *testing.T) {
 				UserDefined: map[string]string{"X-Minio-Internal-compression": compressionAlgorithmV2,
 					"content-type": "application/octet-stream",
 					"etag":         "b3ff3ef3789147152fbfbc50efba4bfd-2",
-					crypto.SSEIV:   "yes",
+					crypto.MetaIV:  "yes",
 				},
 			},
 			result: true,