Add Puma plugin

[jacob-carlborg-apoex]

This manages the Dartsass watch process from rails server.

Most of this is taken from https://github.com/rails/tailwindcss-rails.

[northeastprince]

@dhh could we get this merged?

[dhh]

We've doubled down on bin/dev using foreman to do this. Appreciate the work, but I don't think there's enough of a benefit from adding this to warrant the confusion of when you should use this vs another.

[northeastprince]

There doesn't seem to be a way to do that with puma-dev

[dhh]

I wouldn't recommend using that anymore anyway. You can use localhost as a secure domain and just go off the ports. That's what we do at 37signals.

[jacob-carlborg-apoex]

We've doubled down on bin/dev using foreman to do this

I prefer using Puma plugins in favor of Foreman. Then I don't need to use remote debugging to set a breakpoint.

[jacob-carlborg-apoex]

@northeastprince you can just copy this plugin to your application if you want to use it anyway. I've already done that. Just inline the dartsass_watch_command method at line 15 in the plugin, then you only need the file with the plugin.