Add new parameter which define Function App's `publicNetworkAccess`

[georgeOsdDev]

Summary

Function App's publicNetworkAccess property is defined by disablePublicAccessToStorageAccount. It is confusing and fundamentally irrelevant each other.

https://github.com/newrelic/newrelic-azure-functions/blob/master/armTemplates/azuredeploy-eventhubforwarder.json#L686

Desired Behaviour

Function App's publicNetworkAccess should be defined by isolated parameter specifying it

Possible Solution

Add new parameter which define Function App's publicNetworkAccess

Additional context