* dryrun: verify per-branch GHCR tag
* ci: propagate infra-v* tag bumps to template repo
On push of any infra-v* tag, opens a PR in keboola/agnes-infra-template
that bumps the module ref in terraform/main.tf. Auto-merge rules in the
template (Renovate + CI validate + GitHub native auto-merge) land it
without manual work on patch/minor bumps.
Requires repo secret TEMPLATE_REPO_TOKEN (fine-grained PAT with
Contents:write + Pull requests:write on keboola/agnes-infra-template).
Fail-soft: if secret is missing the job is skipped and Renovate on the
template repo picks up the new tag on its next cycle as a fallback.
* docs(onboarding): 'Keeping the template up-to-date' maintainer section
Documents the two mechanisms (upstream release hook + Renovate), the
required repo settings (allow_auto_merge, validate.yml gate), the TOKEN
secret setup, and the one-time setup checklist. Notes the difference
between template repo (auto-merge on) and customer infra repos
(human approval).