Fix github webhook payload detection logic

[chakrit]

The correct value for "package_type" seems to be "CONTAINER" instead of "docker"

I'm not sure how the original author came up with the value "docker", perhaps that was deprecated/obsoleted by GitHub sometime ago? The documentation at https://docs.github.com/en/webhooks-and-events/webhooks/webhook-events-and-payloads#registry_package doesn't mention anything about potential values.

This was a quick-fix to make GitHub webhook works again but I think if there's time, we should change the detection code to be a bit more robust w/r to GitHub changes (i.e. checks on a well-documented key instead)

[chakrit]

Also it looks like you need the "Repositories" permission on the webhook too, otherwise it seems the repository key will not be sent on the webhook payload.

[joebowbeer]

Also change event type s/package_v2/package/ and this will fix #713

Additional references:

• feat: add schemas for registry_package event, update package event with new information octokit/webhooks#747
• package event outdated google/go-github#2033
• https://docs.github.com/en/webhooks-and-events/webhooks/webhook-events-and-payloads#package