WIP: Add inherit to services table

What does this MR do?

Adds a new column to the services table. The column will be used to check if the service inherits settings from an instance level service

Migrations output

== 20200406093806 AddInheritToServices: migrating =============================
-- add_column(:services, :inherit, :boolean)
   -> 0.0012s
== 20200406093806 AddInheritToServices: migrated (0.0013s) ====================

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