Nuget Embedded config
This solution is a proof of concept of how to embed configuration inside a nuget. For simplicity they are json files but stored as txt. It would be a matter of parsing. It could be xml or whatever.
The files can also be stored as binaries or whatever the user chooses, but then you have to read a byte[] with streams instead of just using a text file, which is usually used for configurations.
Of course you should never store connection strings, passwords or anything sensitive unencrypted.
In the NugetProject / Properties / Resources is where the configuration files are stored.
There is one project that consumes the dll (DllConsumer) and another one that consumes the nuget (NugetConsumer). Also the Nuget is calling to another dll with embedded resources inside.
Remarks
NugetConsumer only works if you add the nuget to a repository of your own, I used my local machine and didn't upload the nupkg to nuget.org because this is just a POC.