make send-request and compute accept plain json

this MR make the send-request and compute commands accept plain yaml or json data, i.e. you can now do something like

python -m my_backend_module compute '{func_name: "version_info"}'

and

python -m my_backend_module send-request '{func_name: "version_info"}'

as well as

python -m my_backend_module send-request some_request_in_a_file.yaml
python -m my_backend_module compute some_request_in_a_file.yaml