Support for asset retries, and deleting existing releases

[nsjames]

Hey there, we're using this internally for some CI operations that take a considerable amount of time (5 hours) where this action is the last step of that process.

We ran into a GitHub downtime right as it came time to create the release and the upload assets failed only due to connectivity issues and since there is no upload retry mechanism we ended up having to do another 5 hour CI build.

We've added an option to retry asset uploads along with the ability to set an interval between retries.

Additionally we've added a delete_on_existing option to allows us to completely regenerate a release each time we run CI.

[softprops]

Thanks for the pull. there's actually an oktokit plugin that implements this for you. If possible I'd love to use this as the standard approach before implementing a custom retry implementation.