perf: enable active record connection pool reaper (#10866)

The pg_stat_activity data showed a lot of idle connections. This affects the total number of database connections available which resulted in production incidents during the weekend.

> reaping_frequency: frequency in seconds to periodically run the Reaper, which attempts to find and recover connections from dead threads, which can occur if a programmer forgets to close a connection at the end of a thread or a thread dies unexpectedly. Regardless of this setting, the Reaper will be invoked before every blocking wait. (Default nil, which means don't schedule the Reaper).

Ref: https://api.rubyonrails.org/v5.1/classes/ActiveRecord/ConnectionAdapters/ConnectionPool.html

config/database.yml

@@ -5,6 +5,9 @@ default: &default
   port: <%= ENV.fetch('POSTGRES_PORT', '5432') %>
    # ref: https://github.com/mperham/sidekiq/issues/2985#issuecomment-531097962
   pool: <%= Sidekiq.server? ? ENV.fetch('SIDEKIQ_CONCURRENCY', 10) : ENV.fetch('RAILS_MAX_THREADS', 5) %>
+  # frequency in seconds to periodically run the Reaper, which attempts
+  # to find and recover connections from dead threads
+  reaping_frequency: <%= ENV.fetch('DB_POOL_REAPING_FREQUENCY', 30) %>
   variables:
     # we are setting this value to be close to the racktimeout value. we will iterate and reduce this value going forward
     statement_timeout: <%= ENV["POSTGRES_STATEMENT_TIMEOUT"] || "14s" %>