The previous resolution would favour one `Oid` over another, due to
the call to `Option::or`.
This was found to result in scenarios where an identity document being
advertised was older than the identity document that the fetching node
already has, and would not fetch namespaces by newly added delegates.
The resolution logic is updated to handle all cases for these `Oid`s,
and when they are both present, uses a commit graph check to see which
one is the latest.
An e2e test is added to check ensure behaviour works correctly.
b5e8776efd