simplify CI config, add source label to docker image

.github/workflows/docker.yaml

@@ -18,7 +18,7 @@ jobs:
       attestations: write
     env:
       REGISTRY: ghcr.io
-      IMAGE_NAME: jaredallard/overlay
+      IMAGE_NAME: ${{ github.repository }}
 
     steps:
       - name: Checkout

Dockerfile

@@ -1,5 +1,6 @@
 # Used as the base image for elint and updater.
 FROM gentoo/stage3
+LABEL org.opencontainers.image.source="https://github.com/jaredallard/overlay"
 WORKDIR "/src/updater"
 
 RUN export MAKEOPTS="-j$(nproc)" && \