Make the backoff time configurable
Description
Currently, GitLab Runner has a built-in backoff (not sure if this is the right term for this specific feature) where it will stop trying to connect to a GitLab instance due to a connection issue.
One of our customers always encountered this behavior when they are doing maintenance with their GitLab instance. It takes approximately 60 minutes before GitLab Runner tries to connect to the instance again.
They are interested in configuring it so that it takes less time for GitLab Runner to wait before connecting to GitLab.
Proposal
Make the max backoff time configurable.