Rebase onto f33fbcf701c824aaf43fd0f439cab30865897364 from upstream

[nataliejameson]

Bi-annual rebase is in effect! This pulls in all of the changes from upstream and puts us at 0.49.5

This includes the commits from:

• 34ab3ab
• 1e29282
• 69d1711
• f8cd359
• [octocrab] Allow committer to be Author *or* GitUser #4
• [octocrab] Use CommitAuthor instead of GitUser/Author in Commit #5
• [octocrab] Add support for 429 headers that github returns #6
• [octocrab] Expose get_links from page module #7

With some various changes to make them work (or to remove the changes if they're now irrelevant) with upstream.

Main things to call out:

• The retry code changed a bit. Before we returned a future of the retryconfig, and now we mutate the ints in place, and then return future<()>
• Some logic to handle "sometimes null, sometimes an empty dict, sometimes who knows what" was implemented upstream. It's no longer needed
• There was some work upstream around something similar to the CommitAuthor changes that we had, however, I'm not sure I trust even the reduced set of fields from "SimpleUser" to be simple enough, so I left what works, over having to go do real prod testing against some random commits that we've run into.

[denbeigh2000]

i have thoroughly reviewed the entire ~14k line changeset, and it lgtm 👍

[nataliejameson]

git push origin -f nmj/rebase-octocrab:discord
Total 0 (delta 0), reused 0 (delta 0), pack-reused 0 (from 0)
To https://github.com/discord/octocrab.git
 + 05b4071...a27e4b2 nmj/rebase-octocrab -> discord (forced update)

discord branch is up to date