Make Commanders run any executable?

I think we should run a second process on the bitcoin nodes, which will simply watch a directory for executables, and run them when new ones are detected.

This watches `/tmp/watchdog` and runs whatever it finds there (#dangerzone).


This is of course fun, but also we can use it to generate random network activity without requiring the RPC server to co-ordinate _everything_ using synchronous JSONRPC calls over http (zzzzzz)...

Someone already made a nice python lib to do this, so the code ends up pretty [simple](https://github.com/willcl-ark/warnet/blob/9cbc88e5d8cfedbe8c417c056c4e2f815891c03c/scripts/file-executor.py).

I know it _sounds_ like a terrible idea, but I think it might actually be quite useful! The only issue is that we _may_ want to add a gpg sig file or something if we had this during an attack day, as we wouldn't last long with folks dropping in auto-executed files...

Thoughts?