Add GitHub Actions to deploy to wordpress.org

[claytoncollie]

Addresses #102

deploy-plugin is triggered when you make a new GitHub release. The action will deploy to wordpress.org and also make a zip archive attached to the GitHub release assets. Makes it easy for people to download the latest release from GitHub. The main thing you need to remember when making a release is to bump the version in the intervention.php file.

update-assets is when you push a change to the .wordpress-org directory or the readme.txt file. This is mainly used to update your "Tested up to" version so that the "plugin is out of date" notice does not show on the wordpress.org profile.

Both of these actions are built and maintained by 10up in case you want to see the different config options.

1. https://github.com/10up/action-wordpress-plugin-deploy
2. https://github.com/10up/action-wordpress-plugin-asset-update

Before these actions work properly, you need to:

1. Create 4 image files and drop them into the .wordpress.org directory. Examples can be found here.
2. Create a zip archive of the plugin and submit to wordpress.org manually. I am a little hazy on the order of this. It has been a while. I can't remember if you submit the plugin then deploy it from GitHub or if the first time you send them a zip archive, it is what they use. I THINK the first time is to just check the plugin files and reserve the name/slug. Have a read over the url I pasted in this step.
3. Add your username and password to GitHub secrets; SVN_USERNAME and SVN_PASSWORD
4. Make a release in GitHub and watch the action deploy to wordpress.org

[darrenjacoby]

@claytoncollie thanks so much for the PR and breakdown. I should have time later in the week and will take a more thorough look. I see you're also working at 10up, I'm joining next month 😊

[claytoncollie]

10up is a great place to be. You'll fit right in!