Reduce the number of necessary parameters when using ILP Auth

[javier]

As per this issue on the C/Rust client library, the python implementation shouldn't need to use 4 parameters to establish an ILP authenticated connection, but only 2: kid and d.

Once updated (guess it depends on the base library to be fixed) the examples in the docs should be updated

[amunra]

This is not really possible due to the library we use in Rust. Same would apply if we were to move to openssl (which would bring non-trivial additional complications). Let's close this.