Migrate to official dotnet for RENODE instead of mono

Dotnet is fully open source, more up-to-date than mono, and available on Ubuntu, and Renode works well with dotnet. 

Dotnet install: https://learn.microsoft.com/en-us/dotnet/core/install/linux
Use the dotnet portable version of renode: https://github.com/renode/renode/blob/master/README.md#installation

I'll provide a PR.