Automatically build branch release images

As of July 31, 2026, a Temporal employee needs to manually run a Github Action in the private temporalio/saas-cicd repository in order to build the release branch images of temporal-worker-controller used in our internal testing environments.

There are two problems with this:

1. External contributors have no visibility into this required step nor ability to run the Github Action.
2. It's a manual action that needs to be performed

This issue is about automating this step of our release process (addressing (2) above). We should be able to automatically kick off the publish-image Github Action in the temporalio/saas-cicd repository when a Git tag is pushed to a Git branch named release/XXXX on the temporalio/temporal-worker-controller source code repository.

See here for instructions of this part of our release process.