Add a durable LogEntries sink like DurableLogglySink

[buzzware]

Serilog and LogEntries, especially with its Live Tail feature would be a great tool for Xamarin mobile development if it had a durable sink. Network connections are unreliable on mobile, and phones switch from WiFi to 4G and back, especially when developing a location monitoring app. Currently, lines are dropped when there is no connection.

A durable sink would use file based storage and then send any stored lines when the network is restored before sending new lines directly.