Security resolver and health checker (#2281)

* Setup health check

* Security health checker cron

* Use resolver throughout codebase

* Use resolver for trade builder

* Add security health checks to schedule

* Handle no provider

* Lint fixes

app/models/market_data_importer.rb

@@ -22,7 +22,8 @@ class MarketDataImporter
       return
     end
 
-    Security.where.not(exchange_operating_mic: nil).find_each do |security|
+    # Import all securities that aren't marked as "offline" (i.e. they're available from the provider)
+    Security.online.find_each do |security|
       security.import_provider_prices(
         start_date: get_first_required_price_date(security),
         end_date: end_date,