EE: Validate that foreign keys are created

What does this MR do?

EE version of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22808

This MR adds a test to validate that each foreign key added has a corresponding index.

This also ensures that an FK is created for every column ending with _id. This does not try to solve existing columns, but rather adds it to the list of ignores.

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/50875

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• EE specific content should be in the top level /ee folder