Support default configuration file

[vincent-psarga]

Most people starting with Hiptest-publisher use the "as a service" version that's inside Hiptest and have a configuration file named "hiptest-publisher.conf" available.

The idea would be that, if the -c|--config-file option is not provided and that there is a file named "hiptest-publisher.conf" in the current directory, hiptest-publisher will use it as a default config file.