Add assets for WordPress.org deployment via GitHub Actions

[jeffpaul]

Is your enhancement related to a problem? Please describe.
As originally suggested in 10up/plugin-scaffold#100, we might want to consider adding the necessary files to deploy plugins to WP.org. Before I dig deeper into submitting a PR here, is that something that would be desired since this is mostly (only?) useful for publicly released plugins?

Describe the solution you'd like
Likely mimicking most of 10up/plugin-scaffold#104 here in https://github.com/10up/wp-scaffold.

Designs

Describe alternatives you've considered

Additional context
This sort of example boilerplate plugin info has been requested here as well: 10up/action-wordpress-plugin-deploy#11.

[darylldoyle]

@jeffpaul I wonder how often the scaffold is used to release plugins on WP.org. Since the additions are relatively small, what do you think about adding something to /docs instead to outline how to do this?

The goal, IMO, is to keep the scaffold as lean as possible to enable engineers to focus on business logic. I do think this would be helpful in a wiki article or the /docs though.