gatsby-cli: Consider exposing Reporter For Use By Starters and Plugins

[Undistraction]

Using the reporter is a nice way to keep logging consistent, but it isn't exposed by gatsby-cli. I think it is worth exposing it or moving it to a separate consumable package.

It can be used by reaching in to lib: const reporter = require('gatsby-cli/lib/reporter'); which is fragile.

[jquense]

the reporter is exposed to plugins via the plugin api (https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby/src/utils/api-runner-node.js#L76) I think this is probably safer than everyone requiring a singleton package. especially if we want to tweak or change how this is handled (or make them pluggable)

[Undistraction]

That's great. I'd missed that and it's definitely useful for plugins, however, it would be nice to have access to it in gatsby-nodeand any related code, for example to report on the creation of pages, tags etc.

I'm working on a starter that has a simple user-facing config that exposes some of the plugin options in a way that's easy to tweak (and allows the user-facing config to be validated). This means I build gatsby-config on the fly depending on what the user has enabled. Again, it would be great to have access to the reporter here.

It just seems silly to have to use a separate logger in these instances which I think are equally valid uses.

Another use would be in functional helpers, like the one that handles pagination.

[KyleAMathews]

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