document how to restart NX2 to NX3 migration when NX3 is not using OrientDB

The steps for restarting a migration from scratch attempt from NX2 -> NX3 are not updated to talk about what needs to be done to the NX3 instance when migrating to NX3 Postgres directly ( or for even H2).

These steps need to be updated to precisely explain what needs to be done in these cases.

https://help.sonatype.com/repomanager3/installation/upgrading-from-nexus-repository-manager-2/upgrade-procedures#UpgradeProcedures-RestartinganUpgrade

Expected

Detailed Instructions for restarting NX2 -> NX3 upgrade under these scenarios:

• NX2 direct upgrade to NX3 using H2 database
• NX2 direct upgrade to NX3 using Postgres database