Update VulnerableCode on AP server PUSH

This is a follow up from https://github.com/aboutcode-org/federatedcode/issues/15 here for VulnerableCode only:

In a decentralized scenario, there are two or more servers cooperating. Here I would like to start building this multiserver architecture. Specifically, we should build an application to run in a second VulnerableCode server that can receive updates notifications from the FederatedCode ActivityPub server for a package and then fetch the data from the backing git stores. And use this to update this separate VulnerableCode instance, including minimally reconciling conflicts.

- #55
- #56