ZipArchive is the part of the official PHP images as of version 5.6. Since I don’t know anything about your image, I can’t say much, because the installation depends on the actual image.
Since your comment in your Dockerfile indicates that the image is based on the official image or at least similar to that, if the zip extension is missing, you should be able to install it the same way as mysql, except you probably don’t need to enable it. This is how I did it:
Although it was probably not necessary for me.