Consistently treat tinyint(1) fields in message database as booleans (#2380)

* Update mysql2 query call to cast booleans

* Treat messages:held field as boolean

* Treat messages:inspected field as boolean

* Treat messages:spam field as boolean

* Treat messages:threat field as boolean

* Treat messages:bounce field as boolean

* Treat messages:received_with_ssl field as boolean

* Treat deliveries:sent_with_ssl field as boolean

app/models/server.rb

@@ -134,7 +134,7 @@ class Server < ApplicationRecord
   end
 
   def held_messages
-    @held_messages ||= message_db.messages(where: { held: 1 }, count: true)
+    @held_messages ||= message_db.messages(where: { held: true }, count: true)
   end
 
   def throughput_stats