Implement mechanism to avoid secondary rate limit on PR creation

[serena97]

Implement timeout, retryAfter and sequential request mechanism to avoid hitting the secondary rate limit, which blocks you from creating more PRs, and repeatedly hitting the rate might result in banning of your app.

Error: You have exceeded a secondary rate limit and have been temporarily blocked from content creation. Please retry your request again later.

The mechanism was built upon the best practice to avoid secondary rate limit

1. Sequential PR creation request - Make requests for a single user or client ID serially. Do not make requests for a single user or client ID concurrently.
2. Retry After - When you have been limited, use the Retry-After response header to slow down. This change allows for retries to handle the creation of the subsequent PRs
3. Time out - Please create this content at a reasonable pace to avoid further limiting

Without this mechanism, I was only able to create 10 PRs and then nori will error out with the secondary rate limit. With this mechanism, I was able to successfully create 61 PRs in one go with nori. We need this change as the GitHub API has recently changed to be more defensive with its secondary rate limit, as seen in other projects

[ivomurrell]

This all looks sensible and I'm glad to hear it fixed the timeout issues you were having! Just one concern about infinite retries and a small nitpick but otherwise all good.

Closes #149 and #155 (lol that doesn't work in comments apparently, I've linked the issue manually instead.)