Option to skip pages created via filesystem routing

[tsdexter]

Maybe I missed it, but it looks like in order to continue using the filesystem route instead of resorting to createPage, I need the ability to skip some pages created with the filesystem routing API.

In one of my use-cases, we have some pages in our CMS that need to be kept around to maintain child pages URL hierarchy. For example, we want to keep /news-events/all-events/some-event-page which gets it's URL from it's parent->child relationship, however we want to redirect /news-events -> /news-events/all-events however, we get the issue:

warn There are routes that match both page and redirect. Pages take precedence
over redirects so the redirect will not work:
- page: "/news-events/" and redirect: "/news-events/" ->
 "/news-events/all-events/"

I know that we can query allWpPage in gatsby-node.ts and loop over the results and then use the createPage API with some logic to check for matching fromPaths in our redirects.json file and create only the non-redirected pages that way. However, the filesystem routing API is more concise and easier to reason about for others coming onto the project.

It would be great if we could add logic to the config export, similar to how you conditionally add DSG for filesystem pages such as:

import redirects from "./redirects"
export async function config() {
  // Optionally use GraphQL here
  return ({ params }) => {
    return {
      defer: true,
      skip: redirects.find(r => r.fromPath === params.uri)
    }
  }
}

The new optional skip property which defaults to false would cause Gatsby to not create a page for this URI at all.