Add default layout look up using findUp

[stenehall]

Changes

Add support for a default layout (default.astro) file in the folder or a parent directory.

The exclude in snowpack-plugin.cjs doesn't actually work and I'm getting an error.

   FAIL  Plain Markdown tests  "Builds markdown pages for prod"
    The "chunk" argument must be of type string or an instance of Buffer or Uint8Array. Received an instance of Object

If the default.astro file is moved one folder up it starts to work tho.

Testing

Added a test to check if this is loaded in the plain-markdown.test.js test.

Docs

Docs needs to be added for this.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 66f7b97

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[vercel]

@stenehall is attempting to deploy a commit to the Pika Team on Vercel.

A member of the Team first needs to authorize it.

[vercel]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployments, click below or on the icon next to each commit.

astro-www – ./

🔍 Inspect: https://vercel.com/pikapkg/astro-www/Hth8tjenshFk5UKnubYVFMoi7U9T
✅ Preview: https://astro-www-git-fork-stenehall-default-layout-take2-pikapkg.vercel.app

[FredKSchott]

This is a good start! You can follow along the issue here: #397

right now @natemoo-re is working on how components in markdown will work, and it has overlap here. Both need the way to say "here's a default thing if none is defined". So I think we want to wait for Nate's work to be ready before we can commit to a design here.

Going to close this until its actionable, but looking forward to picking this up when its ready (hopefully later this week!)