v2: allwo to define CSR file path by argument
As suggested on Github PR #2 by @Gigadoc2, this merge request add a way to set CSR file path on command line instead of using the configuration file.
This option allows the user to share exactly same configuration file on multiple servers and let each server manage their own CSR file.
So, you can have one setup of ACME key and TSIG key which can be used on different servers.