feat(docz-core): auto open browser when start dev mode

[fi3ework]

Description

Auto open bowser when running dev mode(just like create-react-app). Or we could determine if auto open browser in command, such as docz dev -o. For now, I made it as default cause auto-open directly might be more in line with the intuition.🤗

[Glazy]

Nice @fi3ework! 🔥

Not sure what @pedronauck thinks (?) but I think it would be good to introduce this functionality behind a flag like you suggested (-o) 👍

[pedronauck]

I think that since this feature is something native in webpack-dev-server we could have some argument like -o, but just use the flag to set the option like that:
https://webpack.js.org/configuration/dev-server/#devserveropen

[fi3ework]

hi @Glazy @pedronauck 🤗:
I made it optional now, the argument to enable it is docz dev --open or docz dev -o. But for now still not use the native open browser method from webpackDevServer. The current open browser file is copied from create-react-app. I guess this custom open function might be more robust and reliable than the native open browser method from webpackDevServer(not confirmed, just speculate). Any suggestions for improvement?

[fi3ework]

I took a closer look at the code, may it's better to implement openBrowser in plugins, just adjacent to friendlyErrors 🤔