ci: add comments and labels to ghcr.yml tagging

- add comments to clarify short SHA and latest tagging types
- include labels field for Docker image metadata

Signed-off-by: mingcheng <mingcheng@apache.org>

Author: mingcheng

.github/workflows/ghcr.yml

@@ -61,7 +61,7 @@ jobs:
             type=semver,pattern={{major}}.{{minor}}
             type=semver,pattern={{major}}
             # Tag with short SHA
-            type=sha,prefix={{branch}}-,format=short
+            type=sha,format=short
             # Tag latest only on main branch
             type=raw,value=latest,enable={{is_default_branch}}
           labels: |