Create Options Page

[gregrickaby]

I don't want to depend on ACF Pro to handle the options page.

User Stories

• As a site admin, I want to be able to set my custom 404 page from a dropdown of all pages.
• As a site admin, I want to be able to set my HEADLESS_FRONTEND_URL in a text field.
• As a site admin, I want to be able to set my WORDPRESS_PREVIEW_SECRET in a password field.
• As a site admin, I want to be able to set my GRAPHQL_JWT_AUTH_SECRET_KEY in a password field.

Requirements

• Create a simple options page powered by the wds_headless theme
• The options page settings needs to be available in GraphQL. Here is the current query used on the frontend:

query AdditionalSettings {
  headlessConfig {
    additionalSettings {
      error404Page {
        ... on Page {
          slug
        }
      }
    }
  }
}

[tommcfarlin]

This issue will be split into three features branches:

1. The options page to read values from wp-config.php and populate the options page or read form values and save them.
2. Introduce GraphQL support.
3. Replace all ACF-required support so that this options page will be the only feature needed.