feat: Add support to enable backoff when rate limited by the Github API

[andrewhibbert]

Adds support to backoff when a rate limit error occurs as per handle rate limit errors appropriately:

• If the retry-after response header is present, you should not retry your request until after that many seconds has elapsed.
• If the x-ratelimit-remaining header is 0, you should not make another request until after the time specified by the x-ratelimit-reset header. The x-ratelimit-reset header is in UTC epoch seconds.

• [N/A]When introducing a new scaler, I agree with the scaling governance policy
• I have verified that my change is according to the deprecations & breaking changes policy
• Tests have been added
• Changelog has been updated and is aligned with our changelog requirements
• [N/A] A PR is opened to update our Helm chart (repo) (if applicable, ie. when deployment manifests are modified)
• A PR is opened to update the documentation on (repo) (if applicable)
• Commits are signed with Developer Certificate of Origin (DCO - learn more)

Fixes #6643

Relates to kedacore/keda-docs#1557

[zroubalik]

This is great addition, I wonder whether we should try to add this capabilities to all scalers that use HTTP client to optain metrics?

WDYT @kedacore/keda-maintainers

[zroubalik]

/run-e2e github
Update: You can check the progress here