New front matter option to tell Gatsby to not build / publish a page

[imchairmanm]

Currently, we have an option called hidePage: true that I can add to articles to make them ignored by the fancy auto-generated side navigation bar. They're still accessible if you go directly to the page, which is exactly what we want in some cases.

However, since I'll be porting a lot of content from PostgreSQL to MySQL soon, I want to be able to lay out dummy files in a hierarchy within that section early so I don't need to keep renaming and shifting files around as I add new content. In this case, it'd be helpful if I could use an option to signal to Gatsby that it can completely skip the page when building or publishing the content. This way, I could establish the content structure in the directories ahead of time, but not impact SEO, leak incomplete content, or confuse any web crawlers that might happen across the content before it's "ready".

So an option like skipBuild: true or something similar would help me commit work to the repository that doesn't yet affect the published content.