Add an initialRun option to watch to run the watched command first before starting the watcher

[MrSimmmons]

Context: I'm using Lerna V8.1.8, but I know its just nx under the hood.

I've run into this a few times, I start lerna watch running a build command, start my application, then find that the application that I've started is still using the last build from before I switched branches.

So I want to propose a new flag for the watch command (which would also need to be exposed to the lerna CLI as well for the next version of that) of --initial or -i which will run anything after nx watch -- initially before actually starting the watcher.

That way, in this scenario, if I want to switch branches I would just run yarn dev which is lerna watch -i -- yarn run build and my application will build, then the watcher is started and will re-build on any file change.

Would be a nice QoL addition