gocbcore 'SetMetaEx' should optionally accept a collection id

In the backup/restore tooling we are using a 'StreamObserver' to handle events from a DCP stream, the 'Mutation/Deletion/Expiration' callbacks all provide the 'collectionId'; this is in contrast to the 'SetMetaOptions' which accepts a 'CollectionName'. In backup/restore we would like to avoid doing lookup translations for each and every mutation/deletion/expiration that we receive/send.

Solution:
SetMetaOptions accepts both a collection name/id and prioritises one over the other or uses both when applicable.