Cli: Automatically open browser to netlify dev port on `netlify dev`

[DavidWells]

Many users internal & external have reported issues with running netlify dev where the logs saying where the netlify dev server is running disappears.

This leaves the user in a state where they cannot proceed and open/dev their app.

This has been seen effecting create react app & gatsby projects.

- What is the current behavior?

There is a log message that gets erased by certain tools (CRA/Gatsby)

This leaves the users wondering where the netlify dev app is actually running

- If the current behavior is a bug, please provide the steps to reproduce.

- What is the expected behavior?

Automatically open the default browser (and re-use tab if one already is open). This is the behavior of create react app and its a nice DX.

So:

1. Print the message "Netlify dev is now running on port:whatever"
2. Then automatically open the dev app in the default browser

[rlfrahm]

This is the top result on Google when looking to disable this behavior so posting solution to disable here. I ended up holding my version for a while until I finally found that you could just add autoLaunch = false to [dev] in netlify.toml.

Like so:

[dev]
  autoLaunch = false

Reference: https://github.com/netlify/cli/blob/master/docs/netlify-dev.md#netlifytoml-dev-block