Add a model for storing image and video metadata for uploaded files.
Metadata is extracted using ExifTool. You will need to install ExifTool
after this commit. ExifTool 12.22 is the minimum required version
because we use the `--binary` option, which was added in this release.
The MediaMetadata model is separate from the MediaAsset model because
some files contain tons of metadata, and most of it is non-essential.
The MediaAsset model represents an uploaded file and contains essential
metadata, like the file's size and type, while the MediaMetadata model
represents all the other non-essential metadata associated with a file.
Metadata is stored as a JSON column in the database.
ExifTool returns all the file's metadata, not just the EXIF metadata.
EXIF is one of several types of image metadata, hence why we call
it MediaMetadata instead of EXIFMetadata.
Make nokogiri use the bundled version of libxml2 instead of the system
version. In the past installing nokogiri was slow because it had to
compile the bundled version of libxml2, which is partly why we switched
to the system library. Now it's faster because the bundled version comes
pre-compiled with the nokogiri gem.
https://nokogiri.org/#native-gems-faster-more-reliable-installation
Reverts 440bbbb28.
Fix the ca-certificates package not being installed inside the base
Docker image. This caused uploads from HTTPS sites to fail because TLS
certificates couldn't be validated.
* Optimize Dockerfile to minimize size of the Docker image.
* Specify exact versions of important dependencies (Ruby, Node, Vips) to
ensure our dependencies are up to date and locked to known versions.
* Install Vips from source because the version that ships with Ubuntu is too old.
* Install FFmpeg from source because otherwise using the Ubuntu package
pulls in tons of video libraries we don't need, bloating the image.
