* ci: first attempt at adding a gated docker PR Publish (#1038)

* ci: first attempt at adding a gated docker PR Publish

* See if we can use contexts to inject variables after approval

* fix build command

* try alternative context

* docs: pull request template that spells out PR checklist

* change context back to Docker Hub

* Switch optional approval to another workflow

* Make docker builds faster

* Update .github/PULL_REQUEST_TEMPLATE/pull_request_template.md