I’m not sure if there was ever an official docker container released for Sensu Core under the Sensu namespace at docker hub. You are most lilkely using a community contributed docker image for Sensu Core.
Translating existing Sensu Core configs is still partly a manual process, the translator gem helps to some extent but you’ll definitely need to transition workloads manually.
I personally don’t think it makes sense to have the translator in a dedicated Docker image, though someone could produce one easily as the translator really is just an aid in a migration process and not a fully automated task.
If you are planning to migrate to Sensu Go, I’m not sure there is much value in first upgrading to Sensu Core 1.8. But if you are planning to stick with Sensu Core and help interested external community maintain a forked version of the codebase, then I think it makes since to upgrade to Sensu Core 1.8 before EOL so you can be prepared to help the code transition as an external community maintained codebase.
With regard to migrating to Sensu Go, i would recommend that you stand up Sensu Go in parallel with your Sensu Core configuration during the transition, so you can migrate workloads without disrupting your existing alerting. The Sensu Core service elements will not conflict with the Sensu Go backend. And it is possible to run a Sensu Core client side by side with a Sensu Go agent as long as they aren’t both trying to use the same local event port.