Promotionsteps don't take current freight into account for generating commit messages

[Sebast1aan]

Checklist

• I've searched the issue queue to verify this is not a duplicate bug report.
• I've included steps to reproduce the bug.
• I've pasted the output of kargo version.
• I've pasted logs, if applicable.

Description

When using the promotion step helm-update-image or yaml-update to update more than 1 image, the commit message will always indicate that all images were updated, even if some images remain identical between promotions.
Note that this has no impact on what is deployed, so I consider this as a minor issue. It rather improves the git logs to show only which images really changed between promotions.

Screenshots

yaml-update:

helm-update-image:

Steps to Reproduce

Create following Project:

apiVersion: kargo.akuity.io/v1alpha1
kind: Project
metadata:
  name: kargo-test

Create following Warehouse:

apiVersion: kargo.akuity.io/v1alpha1
kind: Warehouse
metadata:
  name: kargo-test
  namespace: kargo-test
spec:
  subscriptions:
  - image:
      repoURL: public.ecr.aws/nginx/nginx
      semverConstraint: ^1.26.0
      discoveryLimit: 5
  - image:
      repoURL: public.ecr.aws/docker/library/golang

Create following Stage:

apiVersion: kargo.akuity.io/v1alpha1
kind: Stage
metadata:
  name: test
  namespace: kargo-test
spec:
  requestedFreight:
  - origin:
      kind: Warehouse
      name: kargo-test
    sources:
      direct: true
  promotionTemplate:
    spec:
      steps:
      - uses: git-clone
        config:
          repoURL: $GITHUB_REPO_URL
          checkout:
          - branch: main
            path: ./src
      - uses: yaml-update
        as: update-value
        config:
          path: ./src/environments/dev/builds.yaml
          updates:
          - key: global.solution.buildnumber
            value: ${{ imageFrom("public.ecr.aws/nginx/nginx").Tag }}
          - key: global.project.buildnumber
            value: ${{ imageFrom("public.ecr.aws/docker/library/golang").Tag }}
      - uses: git-commit
        as: commit
        config:
          path: ./src
          messageFromSteps:
          - update-value
      - uses: git-push
        config:
          path: ./src

Wait for Freight to be generated containing the latest images of both containers. Then manually create new Freight, but change the image for only one of the 2 containers. When promoting this new piece of Freight, you will see that the commit message indicates that both images have been updated.

Version

Kargo main branch

[Sebast1aan]

I'm interested to work on this issue, but might need some input.

Investigation

For helm-update-image this seems to be the relevant function:
func (h *helmImageUpdater) generateImageUpdates(..)

When an image of a promoted piece of Freight is identical to the image in the Freight that is currently being used, this probably shouldn't be part of the updates. I didn't immediately see a quick reference to the Freight that is currently being used for the Stage, so feel free to give some input.

For yaml-update the updates are generated directly within this function:
func (y *yamlUpdater) runPromotionStep(...)