Add the reference published year as a string to meta to preserve any suffixes

[will-byrne]

Fix for https://github.com/elifesciences/enhanced-preprints-issues/issues/815

Adds the unprocessed year published string to the meta if it is present to preserve the suffix without requiring a schema change.

[nlisgo]

My suggestion is that we just store string in meta.yearPublished if it is defined.

if (datePublishedString !== undefined) {
  metaEntries.yearPublished = datePublishedString
}

This will simplify the logic in client too. The only thing tricky in client is to have a fallback id meta.yearPublished is not defined to use datePublished until we do a full reimport.