Add Platform lightup hook

[glennc]

https://github.com/dotnet/core-setup/issues/1597 allows us to do platform lightup on Azure.

We need to implement a hook that allows a server to inject packages and implement a package for Azure App Service that adds the Azure App Service logger.

This issue is for the hook. The implementation would go in the AzureIntegration repo.

[muratg]

@davidfowl when can I review the code? :)

[davidfowl]

I haven't been working on this.

[davidfowl]

Follow up items

• If the application throws and the hosting startup assembly throws the hosting startup errors aren't show in the error page.
• Review error messages and logged error experiences

/cc @glennc