Add GitHub Actions

[jeffpaul]

In order to help automate processes within this repo and for the plugin, we should look to leverage GitHub Actions:

• https://github.com/10up/insert-special-characters/blob/develop/.github/workflows/close-stale-issues.yml
• https://github.com/10up/insert-special-characters/blob/develop/.github/workflows/codeql-analysis.yml
• https://github.com/10up/insert-special-characters/blob/develop/.github/workflows/dependency-review.yml
• https://github.com/10up/insert-special-characters/blob/develop/.github/workflows/push-asset-readme-update.yml
• https://github.com/10up/insert-special-characters/blob/develop/.github/workflows/push-deploy.yml
• https://github.com/10up/restricted-site-access/blob/develop/.github/workflows/repo-automator.yml

[dkotter]

One thing worth noting is this repo is private, so there are limits on GitHub Action minutes that can be used. Is this something that should be discussed with the Mailchimp team prior to implementing these Actions, to ensure we aren't using all of their free minutes (or worse, causing extra charges)?

In addition, there may be a few of these Actions that don't run properly on private repos (Dependency Review I think is one) so we can add those but will need to disable them.