Allow option of pushing data to ha-mqtt-iot instead of polling only

[W-Floyd]

Being able to push data to this tool would improve latency/reduce polling, and allow more complicated tools to be decoupled much easier. I am not a computer scientist, so my immediate thought is to allow using a Unix socket (if available?), or maybe just a file to write the state to. Any accompanying program would then watch the state to take commands.

[W-Floyd]

Some more thoughts on this, while having an option to pipe data in externally and on-demand, a simple method to stream data around using channels would be a good first (and main) step. For cases in which a command produces data quickly and then exits, we can spin up our own recurring function to run it again occasionally. For cases in which the external software would be better suited to periodically sending updates (for example, listening for an event/measurement), we should be able to simply read this new line, and process as needed.