impr(ci): use ghcr.io as the default container registry (#11210)

## Problem
Docker Hub has new rate limits coming up, and to avoid problems coming
with those we're switching to GHCR.

## Summary of changes
- Push images to GHCR initially and distribute them from there
- Use images from GHCR in docker-compose

compute/compute-node.Dockerfile

@@ -77,7 +77,7 @@
 # build_and_test.yml github workflow for how that's done.
 
 ARG PG_VERSION
-ARG REPOSITORY=neondatabase
+ARG REPOSITORY=ghcr.io/neondatabase
 ARG IMAGE=build-tools
 ARG TAG=pinned
 ARG BUILD_TAG