urunc-deploy: Use a specific tag for urunc-deploy container image

[ananos]

At the moment, we use latest as the tag for the urunc-deploy container image (image: ghcr.io/urunc-dev/urunc/urunc-deploy:latest) in urunc-deploy.yaml. This is not entirely correct.

We should use the tag that corresponds to the specific branch. For instance:

• When we push a new commit to main, we should be able to calculate the commit hash of the current tip of main, and use this as the tag to the container image built and pushed using the automated action. This is probably already implemented in:

  urunc/.github/workflows/build-latest.yml

  Line 172 in 70411d2

  # Determine the manifests' TAG

  (kind of).
• When we use urunc-deploy (kubectl apply), we should be able to determine which tag to use. Maybe using kustomize, or some other trick/script to make sure that the tag corresponds to this specific version of the code. The same stands for feature/code altering branches that we would like to test.