feat: extract main generic_sender logic to send() python method

Created by: zlamalp

• Previously all generic processing was part of the __main__, expected to be started from the cmd line only. Now it is extracted to the defined send() method and can be called directly from python scripts too.
• With this solution, we can still use the script from the command line, when __main__ simply checks input and calls send() instead.
• New opts param was added to the send(), so the custom send scripts can extend default transport commands for SSH/cURL.