Replace `communities_new` view function override

• instead, we override the app's config in a way that evaluates the SITE_{API,UI}_URL values and casts them to strings
• because we have configured these values as LocalProxy objects with some logic for dynamically calculating the URLs based on the HTTP request context instead of plain strings, we sometimes ran into typing issues
• the above mentioned logic helps us with having multiple valid domain names (and generating valid links based on which is being visited)