Improve Sidekiq compatibility docs: add "Renaming Worker Class" case
What does this MR do and why?
Was extracted from this discussion: #439738 (comment 1776452247)
Our Sidekiq docs do not cover the case when you need to rename the worker class: https://gitlab.com/gitlab-org/gitlab/blob/b40fab0ecd4e1078067479c9d2cad355efe4cdfe/doc/development/sidekiq/compatibility_across_updates.md#L19
This MR improves the documentation to cover this case.
Relates to #442629 (closed)
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