Avoid using EC_CFG environment variable to setup the ecat-client configuration file

[MMarcus95]

Hello,

when using an instance of the class EcCommonStep to setup the ecat-client, the EC_CFG environment variable is used by default to retrieve the path to the .yaml configuration file.

To improve the portability of the code, it would be really nice to set the path to the configuration file using a different approach, e.g. using a CMAKE variable or defining a constructor for EcCommonStep that takes as input the path to the config file.

Thanks!