Refactor Reenqueuer shared examples

What does this MR do?

Refactors the Reenqueuer shared examples to make them easier to reuse.

• Allow the user to specify args in the perform call
• Use simpler subject instead of worker_class
• Remove the unnecessary let variable rate_limited_method

I originally did this because I was going to reuse Reenqueuer for something, but I changed approach there. So there is no related issue for this one, but it will help future reuses of Reenqueuer.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style 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.