* change retag-and-push behaviour

- add timestamp to tag
- use grep instead of docker pull to check for success

Need to regex the resulting image tag to avoid race condition where the time ticks over between tagging and test.

* test: update to reflect tagging ADR

* feat: implement updated tagging ADR

* doc: clean docker images for local testing

* test: improve clarity

* Use UTC for timestamp

* switch to realistic hashes to help understanding