Cache Package downloads / immutable releases

We were using for years: `maltyxx/images-generator` pkg and this morning nightly discovered that the GitHub repo entirely has been deleted and now returns 404.

In Go there is an [Global Module Proxy](https://proxy.golang.org/), does it maybe make sense to use the existing bunnycdn subscription to do similar things proxy all publicly available packages and make it also in that way immutable that nobody can change it afterwards 🤔 . (I did an quick issue search didnt found).

I mean in SymfonyCon there were also speakings about that you can upload your package directly to packagist 🤔,

The issue names no files, tests, or entry points. Start by reviewing the package download and release behavior relevant to the proposed Global Module Proxy, bunnycdn subscription, and immutable storage. Done would require a decided design and implementation scope for cached, immutable package downloads.

Written by the indexing model from the issue text.