DEV: Add deprecation warning of non-header based API auth

This change adds a message to the admin panel if it detects an api
requests that doesn't use the new header based authentication method.

The message is to warn people to switch to header based auth and links
to the api documention topic on meta for more info.

lib/auth/default_current_user_provider.rb

@@ -283,6 +283,10 @@ class Auth::DefaultCurrentUserProvider
   def lookup_api_user(api_key_value, request)
     if api_key = ApiKey.active.where(key: api_key_value).includes(:user).first
       api_username = header_api_key? ? @env[HEADER_API_USERNAME] : request[API_USERNAME]
+      if !header_api_key?
+        # Notify admins of deprecated auth method
+        AdminDashboardData.add_problem_message('dashboard.deprecated_api_usage', 1.day)
+      end
 
       if api_key.allowed_ips.present? && !api_key.allowed_ips.any? { |ip| ip.include?(request.ip) }
         Rails.logger.warn("[Unauthorized API Access] username: #{api_username}, IP address: #{request.ip}")