Application setting for container policies on past projects

What does this MR do?

This MR adds an Application Setting that allows container expiration policies to be saved on historic projects created before container expiration policies were implemented. This MR does not use the new setting anywhere. That will be implemented in a separate frontend MR.

Database

Migration output:

== 20200331195952 AddContainerExpirationPoliciesEnableHistoricEntriesToApplicationSettings: migrating
-- transaction_open?()
   -> 0.0000s
-- execute("SET statement_timeout TO 0")
   -> 0.0004s
-- transaction()
-- add_column(:application_settings, :container_expiration_policies_enable_historic_entries, :boolean, {:default=>nil})
   -> 0.0024s
-- change_column_default(:application_settings, :container_expiration_policies_enable_historic_entries, false)
   -> 0.0290s
   -> 0.0321s
-- columns(:application_settings)
   -> 0.0267s
-- transaction_open?()
   -> 0.0000s
-- exec_query("SELECT COUNT(*) AS count FROM \"application_settings\"")
   -> 0.0013s
-- exec_query("SELECT \"application_settings\".\"id\" FROM \"application_settings\" ORDER BY \"application_settings\".\"id\" ASC LIMIT 1")
   -> 0.0005s
-- exec_query("SELECT \"application_settings\".\"id\" FROM \"application_settings\" WHERE \"application_settings\".\"id\" >= 1 ORDER BY \"application_settings\".\"id\" ASC LIMIT 1 OFFSET 1")
   -> 0.0004s
-- execute("UPDATE \"application_settings\" SET \"container_expiration_policies_enable_historic_entries\" = FALSE WHERE \"application_settings\".\"id\" >= 1")
   -> 0.0008s
-- change_column_null(:application_settings, :container_expiration_policies_enable_historic_entries, false)
   -> 0.0007s
-- execute("RESET ALL")
   -> 0.0002s
== 20200331195952 AddContainerExpirationPoliciesEnableHistoricEntriesToApplicationSettings: migrated (0.0641s)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team

Related #208735 (closed)