Docs: Add documentation on how to prevent the Global Media Library site from being created

[ntwb]

Add documentation on how to prevent the Global Media Library site from being created

// Disallow Altis from creating a Global Content Repository site
add_filter( 'muplugins_loaded', function() { 
	if ( defined( 'WP_INSTALLING' ) && WP_INSTALLING ) {
		remove_action( 'plugins_loaded', 'Altis\\Enhanced_Search\\load_elasticpress', 4 );
	}
	remove_action( 'altis.migrate', 'Altis\\Global_Content\\maybe_create_site' );
} );

Note: The above code is untested by my, I copied the source from another internal HM project, this source can be looked up for further reference/context

[roborourke]

Why do you need to do this? Just thinking If there is any context for this we may want to document to make it more searchable. Or perhaps we need to consider making it a config option?

I'm not really keen on encouraging doing this at the moment but I'd prefer to use a config option so we could at least determine whether to load any other features that may rely on it in future and warn appropriately.