chore: add workflow to preview docs PRs on Netlify

[amoeba]

Creates a new workflow that publishes the docs to Netlify for PRs that touch paths related to the docs. Some things to note:

• When the deploy runs, a command gets added to the PR (see below)
• New comments aren't made when the preview is re-deployed
• The workflow also attaches a "deploy" to the PR so you can click the "View deployment" button (see below) to preview the page
• This is currently limited to running only on PRs not made from forks. i.e., if you want to update the docs and get previews, you have to push to columnar-tech, not a fork. This is because of the default behavior of secrets and Actions. If we wanted to relax this, we'd need to set up an Environment (I don't have access).

Closes #62

[github-actions]

🚀 Deployed on https://68d70a9eed4a96254a6ee18c--columnar-dbc.netlify.app

[amoeba]

I'm going to try out environments, closing so I can test.