WIP: An attempt to use onnxruntime in RingerSelectionTool

This MR introduces .onnx models and onnxruntime c++ api to work out inference in RingerSelection method for Trigger electrons. RingerSelectionTool currently uses simple DNN but there is the scope of using a more complex model (e.g. CNN). RingerSelectionTool is used in both offline and trigger purposes. This MR particularly focuses on the Trigger environment. This WIP is being done with the collaboration of Rio de Janeiro group (@jodafons , @mverissi ). The starting point of this MR would be AthExOnnxRuntime (example package) and !35042 (closed) (an WIP started by @jodafons ). It is still WIP since few more things needed to be added (also not the high priority of the soon coming feature freeze). However, it is going in the right direction and soon we will be having our first onnxruntime usage for Run 3 data taking. Adding people who would be interested (or I might need their suggestion in future); @afarbin , @dguest , @fernando , @cjmeyer , @christos , @wenaus , @hgray , @tamartin , @akraszna, @fwinkl , @smh