Offline QA: specific configuration of the QA task

The merge request introduces the possibility of the specific QA task configuration withing the QA-config yaml file. In the yaml-file, the configuration should be defined under qa//specific node. On the task side the configuration is represented with a plain structure (Config), which can be defined using the function std::optional CbmQaTask::ReadSpecificConfig() in the task initialization function (for expample see the CbmCaInputQaBase class implementation).

The specific configuration feature is optional and can rely on the default-initialized Config structure, so the "specific" branch of the QA-configuration file is not mandatory.

Additionally, the CbmQaTask interface was modified in order to simplify the usage.