add control plane

[hackaugusto]

Ideally services would be crash first, since that is th easiest model to work with. but unfortunately this won't serve all the servers:

• the store creates in-memory representations of the trees, which will take a bit of time to create, so for that service it is best to avoid restarts
• the rpc server works as a reverse proxy, restarting the service would close all client connections, which is not great for end-user performance
• the current version of the block producer contains only in-memory store of transactions, so restarts would cause issues, eventually this will be lifted, but we should probably avoid losing in-flight transactions if we can

because of the above, we should have a way of managing the servers without requiring restarts. there are multiple ways this can be implemented:

• watch dog over the configuration files, so when the file is written, the server reloads the configuration and applies the changes
  • this is nice and has a neat interface, but it can become an issue for cases were the user introduces syntax errors to the file
• a control socket. this can be a unix socket (file socket), or a proper networked socket.
  • this is a neat approach, usually the socket is hidden behind a CLI program. it can be useful for settings that should not be persisted
• system signals. like sigusr1
  • this is great to integrate the servers with process monitors, works well with systemd and other tools, but we have limited number of signals

I don't think any of the options above are ideal, usually a mix of each gives the best results

[hackaugusto]

for file watching it seems the best option is notify, it is wildly used (see the docs). The only other option I found was watchman, but that requires an external service.

the only downside is that the api seems to be sync, so we should probably nave a file watching "service" running on a separate thread, sending events to the async tasks in tokia via channels. (note: we can make the service unnecessary by watching a single file, that would mean the configuration of all the services should fit in the same file)