Extracts Dockerfile.openldap's `ldapbuild` stage (compile OpenLDAP from
source for the nestgroup overlay, ~5 min, dependent on git.openldap.org
being reachable) into its own Dockerfile, built and pushed to
ghcr.io/theta42/openldap-nestgroup by this workflow whenever the pinned
commit changes.
This commit only adds the new image + workflow; Dockerfile.openldap itself
still compiles from source. A follow-up change switches it to FROM the
published image once this workflow has run once and the image exists.
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
