The letsencrypt-internal ClusterIssuer does not exist on the cluster.
Only letsencrypt-prod and letsencrypt-staging are available.
Both use DNS-01 via Cloudflare for the mk-labs.cloud zone,
so they work for internal-only hosts with no public HTTP reachability.
Fixes: https://github.com/volcengine/openviking/issues/...
Closes: kanban task t_1c2cc2db
