Ci::JobToken::AuthorizationsCompactor

What does this MR do and why?

This MR adds a process to compact Ci::JobToken::Authorizations into the limits of the Ci::JobToken::Allowlist as part of #478540.

I've included comments in the code to explain what it is doing, but please let me know if there are questions or if I can add more details. This approach uses the traversal_ids to find the most common namespaces in the list of projects in the authorization log and consolidates those projects into one entry for the namespace. It repeats this process until the list is below the target size, or raises an error if the target size cannot be achieved.

@fabiopitino @dbiryukov @shampton would you mind giving this a look when you have some time and let me know if this makes sense, or if there are some optimizations I'm missing?

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