Only fall back to master for non-Azure connections on OE database nodes

[Charles-Gagnon]

We currently fall back to master for OE connections if a DB can't be found : https://github.com/microsoft/sqltoolsservice/blob/main/src/Microsoft.SqlTools.ServiceLayer/ObjectExplorer/SmoModel/DatabaseTreeNode.cs#L29

This was originally done for fixing AGs in #854 - but this should only apply for non-Azure connections. This was part of the cause of this issue : microsoft/azuredatastudio#21245 where Azure connections failed querying sys.database_service_objectives and thus fell back to master (which meant displaying the wrong tables and other objects)