Add Open-Mode to extends the possibilities of usages

[PaulRosset]

Do you want to request a feature or report a bug?

Feature

What is the current behavior?

The Open-Mode has the goal to extends the possibilities by using only the crucial information of the size of the build and nothing else, thus it permits to use this data to create a lot of other things and not only for a CI purpose in case of fail or success depending a maxSize.

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

What is the expected behavior?

Show via a simple console.log() the size of the current build.

If this is a feature request, what is motivation or use case for changing the behavior?

Simply extends the possibilities as cited above, because for now, the tools is restricted to a pass or a failed build. But with the built informations we can do much more.

As an example, with the feature cited above, we can for example use the stdout of bundlesize to let the developers create their own things.

I already can create the pull request to show.