Fix requirements import authorize route to match Workhorse route

What does this MR do?

Related to #246857 (closed)

In !48060 (merged) the new endpoint import_csv was introduced to import Requirements. This endpoint requires Workhorse authorization and the new WH route was added here: gitlab-workhorse!664 (merged).

When implementing the UI changes we noticed that the Rails route didn't match resulting in the following error:

Started POST “/gitlab-org/gitlab-test/-/requirements_management/requirements/import_csv/authorize” for 127.0.0.1 at 2020-12-08 17:20:53 +0000
No route matches [POST] “/gitlab-org/gitlab-test/-/requirements_management/requirements/import_csv/authorize” excluded from capture: DSN not set

This MR fixes the rails route and allows the requirements to be successfully imported from a CSV file.

Screenshots (strongly suggested)

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 to #284138 (closed)