Document how to utilize other Logging services/platforms

Regarding: https://docs.microsoft.com/en-us/azure/azure-functions/functions-monitoring#application-insights-pricing-and-limits

This page should provide information on if/how other platforms can be used "natively" with Azure Functions. i.e. can I, somehow, make ILogger an NLog object? Some other logging platform? If not, it should be called out so customers aren't banging their heads against a wall trying to do it. If so, we should have an example of how to do this.

Posting here [by request](https://github.com/MicrosoftDocs/azure-docs/issues/33443#issuecomment-602787650)

[linking to predecessor](https://github.com/MicrosoftDocs/azure-docs/issues/33443) and [potential duplicate](https://github.com/Azure/azure-functions-host/issues/5178)

cc @brettsam @ggailey777

Start by reviewing the linked predecessor and potential duplicate, then compare their conclusions with the Azure Functions monitoring documentation referenced in the issue. Done means documenting whether ILogger can use other logging platforms natively and, if supported, adding a verified usage example; otherwise, clearly stating the limitation.

Written by the indexing model from the issue text.