Move the metadata parsing code from MediaAsset to ExifTool::Metadata so
we can use it outside the context of a MediaAsset, in particular when
dealing with a MediaFile that hasn't been saved to disk yet.
Bug: if ExifTool exited with status 1 because it thought the file was
corrupt, then we didn't record any of the metadata, even though it was
able to read most of it. It turns out there are thousands of posts with
minorly corrupt metadata that ExifTool is still able to read, but will
complain about.
Fix: ignore the exit code of ExifTool and always save whatever metadata
ExifTool is able to return. It will return an `ExifTool:Error` tag in
the event of errors.
Note that there are some (many?) files that are considered corrupt by
ExifTool but not by Vips, and vice versa. Probably because ExifTool only
parses the metadata while Vips only parses the image data.
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.
