Add Sidekiq job for importing CSV requirements async

What does this MR do?

Related to #249182 (closed)

As a follow up to !46361 (merged), this MR adds a Sidekiq job in order to enable scheduling CSV requirements import and perform it async.

This job would be scheduled in the next iteration MR where we add a GraphQL mutation to import the requirements.

Update: This job would be scheduled in the next iteration MR where we add an API endpoint to import the requirements. (The implementation changed due to lack of support for direct upload in GraphQL uploads. See #246857 (comment 448347386)).

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 #249182 (closed)