suggest that default durability for new nodetype be bronze

[billysug]

The script at https://github.com/jagilber/powershellScripts/blob/master/serviceFabric/drafts/azure-az-sf-copy-nodetype.ps1 created a silver durability nodetype when "copying" an existing bronze nodetype. I suggest it defaults to bronze since you can't go back or default to what the copied one is.