Add support to query NSG flow log retention period from azure_network_watcher.

[rajlearner17]

Currently this query returns only the id of the
select jsonb_pretty(flow_logs) from azure_network_security_group where name = 'myabc-nsg'
[ {
"id": "/subscriptions/xxxxxxxxxxxxxxxxxx1b097a0469dd/resourceGroups/NetworkWatcherRG/providers/Microsoft.Network/networkWatchers/NetworkWatcher_westus/flowLogs/myabc-nsg-flowlog
}
]
However
If we can pull more info from the Flow logs settings from Network Watcher will be good, this will also address the retention period.

API reference - https://docs.microsoft.com/en-us/rest/api/network-watcher/flowlogs/get

Ref Azure CIS 1.3.0 : 6.4