feat: environment configuration

Environment variables can now be used to configure any
config property including the feeds list.

This makes it easier to use in environments without access
to config files like GCR. Some may prefer not to have a separate
config file as well.

Also added build metadata to the docker image and binaries.

.github/workflows/action.yml

@@ -71,6 +71,10 @@ jobs:
           platforms: ${{ steps.set-platforms.outputs.DOCKER_PLATFORMS}}
           cache-from: type=gha
           cache-to: type=gha,mode=max
+          build-args: 
+            VERSION=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.version'] }}
+            REVISION=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.revision'] }}
+            BUILDTIME=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.created'] }}
 
       - name: Docker Hub Description
         uses: peter-evans/dockerhub-description@e98e4d1628a5f3be2be7c231e50981aee98723ae # v4.0.0