Add a last_updated property to MetadataDocuments #51
Description
WordPress plugin and theme listings show a "Last Updated" line. This is currently unavailable when retrieving the metadata for a DID.
- While an aggregator could generate this, that would be based on their last import, which would differ from one aggregator to the next.
- While a ReleaseDocument could store this for a particular artifact, metadata may change without a new artifact being generated.
For parity with dotorg, this would be a datetime string, though any value that strtotime() supports would work.
For example, the client would do this in PHP:
$data->last_updated = gmdate( 'Y-m-d h:ia T', strtotime( $metadata->last_updated ) );