Upload an object

Uploads an object under the specified key and sets the object's headers. In case of simultaneous uploads to the same key, the upload with the last written byte wins. Set the Content-Type header to specify the media type for the object. You can use an MD5 or SHA256 hash as the ETag header for this version of the object to optimize caching. Use the Expires header to specify the time after when the object expires and is automatically deleted. With this operation, you can also set custom headers for the specified object. See Add custom headers.