Add exponential back-off retrying for the github API tools in `generate-release`

[alice-i-cecile]

When using the various methods to interact with Github's API, it's possible to get rate-limited. This is particularly common with the various mutating operations, like opening issues or leaving comments.

Rather than simply aborting due to failure, we should retry, using the standard exponential back-off strategy, up to a max time.

This will make the tool much more reliable to run automatically.