Improve retry logic

[gr2m]

Follow up to #71.

We introduced a simple request retry logic via #79. There are a few ways we could improve the implementation

• do not retry for all response status, compare https://github.com/octokit/plugin-retry.js/blob/266bfeeb75760dd6c59317c28aba9c9b7ace8a81/src/index.ts#L14
• handle rate limit responses retry-after and x-ratelimit-reset headers, compare https://github.com/octokit/plugin-throttling.js
• Implementing custom retry logic without a 3rd party dependency to reduce the bundle size