chore: update self-host image release references (#4136)

## Summary

Stable v4 Docker image builds now also publish `v4` and `latest` tags,
giving Docker-based self-hosters a maintained floating tag to use after
a stable release. The Kubernetes guide now uses the current Helm chart
line and current pinned examples, so new installs and upgrades resolve
to the 4.5 chart line instead of the 4.0 line.

## Design

The publish workflows add the floating tags only for stable `v4.x.x`
image tags. Prerelease and `main` builds keep their existing tags.

.github/workflows/publish-webapp.yml

@@ -76,6 +76,10 @@ jobs:
           # therefore publishes to its own package automatically.
           image_tags=$REF_WITHOUT_TAG:${STEPS_GET_TAG_OUTPUTS_TAG}
 
+          if [[ "${STEPS_GET_TAG_OUTPUTS_TAG}" =~ ^v4\.[0-9]+\.[0-9]+$ ]]; then
+            image_tags=$image_tags,$REF_WITHOUT_TAG:v4,$REF_WITHOUT_TAG:latest
+          fi
+
           # when pushing the mutable main tag, also push an immutable-by-convention
           # full-commit-sha tag so a commit can be resolved to a specific digest
           if [[ "${STEPS_GET_TAG_OUTPUTS_TAG}" == "main" ]]; then

.github/workflows/publish-worker-v4.yml

@@ -76,6 +76,10 @@ jobs:
           ref_without_tag=${IMAGE_REGISTRY}/${STEPS_GET_REPOSITORY_OUTPUTS_REPO}
           image_tags=$ref_without_tag:${STEPS_GET_TAG_OUTPUTS_TAG}
 
+          if [[ "${STEPS_GET_TAG_OUTPUTS_TAG}" =~ ^v4\.[0-9]+\.[0-9]+$ ]]; then
+            image_tags=$image_tags,$ref_without_tag:v4,$ref_without_tag:latest
+          fi
+
           echo "image_tags=${image_tags}" >> "$GITHUB_OUTPUT"
         env:
           IMAGE_REGISTRY: ${{ inputs.image_registry || vars.IMAGE_REGISTRY || format('ghcr.io/{0}', github.repository_owner) }}