[feature request] OpenSSL set cert / key

[bmahlbrand]

I think it'd be rad to add the ability to configure the certificates / key etc for the OpenSSL sessions. Maybe they could be added as arguments to an overload of the constructor, or to the endpoint? Not sure of the clean way to punt these cert / key files to initialization here: https://github.com/Ybalrid/kissnet/blob/b10957609799967df5e146363f3635162f313b4f/kissnet.hpp#L636

[Ybalrid]

If you are still interested, and familiar with the SSL library, I would find it rad to look into a pull request when you add some API for the Kissnet user to do so, this function could take a const reference to a structure containing the relevant parameters that you need to pass in, or anything of that nature....