Fix ClusterApiToken not persisted on secondary after initJoin

[comerford]

See: #1848

• initJoin calls SyncConfigFromAsync → RestoreConfigAsync(isConfigTransfer: true)
• The isConfigTransfer branch filters sessions to only ApiToken, dropping ClusterApiToken
• Token lives in memory after join but is never written to auth.config on the secondary
• On service restart, ClusterManager can't find the token so you get "No API token was found for the Cluster domain"

This is a simple fix to add the ClusterAPI token so it won't get filtered.