Decouple release process from publishing images to mcr

The current release depends on the webhook, proxy and proxy-init images to be published to mcr. In case of any issues, this would require us to revert the release changes (promotion of helm charts, tags, etc.)

We should decouple the release by switching to use ghcr for all the images, so images are built and published immediately.

- [ ] Use ghcr to host the images (webhook, proxy, proxy-init)