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

.github/scripts/generate_image_maps.py

@@ -49,10 +49,10 @@ target_stages = (
 for component_name, component_images in components.items():
     for stage in target_stages:
         outputs[f"{component_name}-{stage}"] = {
-            f"docker.io/neondatabase/{component_image}:{source_tag}": [
+            f"ghcr.io/neondatabase/{component_image}:{source_tag}": [
                 f"{registry}/{component_image}:{tag}"
                 for registry, tag in itertools.product(registries[stage], target_tags)
-                if not (registry == "docker.io/neondatabase" and tag == source_tag)
+                if not (registry == "ghcr.io/neondatabase" and tag == source_tag)
             ]
             for component_image in component_images
         }