public BodyPartBuilder content(File file, int bufferSize) {
        requireNonNull(file, "file");
        return content(file.toPath(), bufferSize);
    }
Adds the specified {@link File} as a body part content.
The specified {@code bufferSize} is used to create a buffer and the buffer is used to read data from
the {@link File}.
core/src/main/java/com/linecorp/armeria/common/multipart/BodyPartBuilder.java