Use child_process node instead of require for cozy-konnector-dev

[ptbrowne]

Since cozy-konnector-dev uses require to "launch" a konnectors' code, require.main === module is false, preventing the use of the if (require.main === module) { main().catch(e => {...}) } technique to prevent the execution of code when importing the file (can be useful to test service functions without splitting the service into a "runnable" file and a "utilify" file). See https://mattermost.cozycloud.cc/cozycloud/pl/1ms91mf3f7rnmcagfymqw45j1c for more context.