FEATURE: add connnection reaping based on maximum age

This feature ensures connections to the db are always attempted to be closed
after 600 seconds of idle time.

config/discourse_defaults.conf

@@ -123,6 +123,8 @@ new_version_emails = true
 connection_reaper_age = 30
 # run reap check every 30 seconds
 connection_reaper_interval = 30
+# also reap any connections older than this
+connection_reaper_max_age = 600
 
 # set to relative URL (for subdirectory hosting)
 # IMPORTANT: path must not include a trailing /