@SuppressWarnings("UnstableApiUsage") // multipart upload uses beta API
    public MultipartUpload initMultipartUpload(String absoluteFilePath, String contentType, Map<String, String> userMetadata) {
        String storageLocation = getStorageLocation(absoluteFilePath);
        BlobMetadata metadata = buildBlobMetadata(storageLocation, contentType, bucketName, userMetadata);
        return blobStore.initiateMultipartUpload(bucketName, metadata, PutOptions.NONE);
    }
Initialize multipart upload

@param absoluteFilePath absolute path according to the bucket, for example: Users/user1/files/input/file.txt
@param contentType      MIME type of the content, for example: text/csv
storage/src/main/java/com/epam/aidial/core/storage/blobstore/BlobStorage.java