Support WordPress' new environment types feature.

[Luke Nelson]

WordPress 5.5 allows you to specify the environment type and and have themes and plugins respond appropriately. https://make.wordpress.org/core/2020/07/24/new-wp_get_environment_type-function-in-wordpress-5-5/

Currently, to use the dev version of simpods with the installer, you have to put this in wp-config:

define( 'SIMPODS_INSTALLER_URL', 'https://398827.vps-10.com/~simpodsdev/simpods-site-staging/wp-admin/admin-ajax.php' );

This new feature would mean that a developer only needs to put

    define( 'WP_ENVIRONMENT_TYPE', 'staging' ); // or development

and simpods would select the correct channel automatically. The benefits to developers would be that if they already have the environment type set, simpods would already have it set. You could still keep the ‘SIMPODS_INSTALLER_URL’ set to overwrite this.