Deprecate this action 💀

[shawnbot]

A lot has changed with Now's GitHub integration since we made this action, and it does all of the things we do. As we migrate our repos from Now v1 to v2, we need to also remove this action from our workflows and add them to the list in our installed app settings. Here's the playbook for migrating:

1. Add the repo in the Now app settings (private, behind sudo auth).
2. Delete any actions with uses = "primer/deploy@..." in .github/main.workflow, and remove that action's name from any needs = [...] prerequisites in other actions.
3. Commit those changes to a new branch and create a PR so that you can see what happens and fix any issues that come up.

That should be it! If all goes well, you'll get a comment from now[bot] with a link to the deployment. If the repo you're updating is on Now v2 (if it has version: 2 in now.json), you'll get an alias URL for the most recent deployment in the form {project}-git-{branch}.primer.now.sh. ✨

Note that migration URLs are still available in the status checks list for each push, but the integration uses our Deployments API and closes #7.

Repos to migrate

• primer/blueprints (underway in Upgrade to Now v2 blueprints#43)
• primer/css (done in Remove primer/deploy action css#809)
• primer/components
• primer/design
• primer/g-octicon (underway in primer/g-octicon#14)
• primer/presentations
• primer/primer.style

Docs to update

• primer/actions (this repo can probably be deleted if we're only using primer/publish everywhere)