PR preview deployments

[MattIPv4]

Feature Suggestion

Feature description

Make use of https://github.com/digitalocean/app_action to enable ephemeral PR preview deployments in the repository. https://github.com/Hacktoberfest/hacktoberfest-2022/blob/main/.do/deploy.template.yaml already exists with the app spec that we're using in staging/production, so we should be able to have the preview workflow make a copy of that and make minor adjustments as needed, and then deploy the PR preview.

How the feature is useful

Allows developers to more easily check that their changes in a PR are working as expected without needing to use the staging branch/environment that is internal to DigitalOcean (though this will still stick around for DigitalOcean developers that need to test against a staging version of the underlying API for Hacktoberfest).