Adapt to 429

Trying out dependabot-gitlab i quickly ran in to 429 issues and started looking at the handling. It seems that it just do an abort / raises an exception

I would like to propose that another approach is used, like eg. python-gitlab uses for handling 429's where it's handled in a retry loop but with delays that defaults to a exponential backoff and if either "Retry-After" or "RateLimit-Reset" headers is present thos are used to calculate the delay

python-gitlab 429: https://github.com/python-gitlab/python-gitlab/blob/main/gitlab/client.py#L722

Headers: https://docs.gitlab.com/ee/user/admin_area/settings/user_and_ip_rate_limits.html#response-headers