fix(backstage): correctly render lightspeed image fields regardless if they are string or map [RHDHBUGS-3091]

[rm3l]

Description of the change

In the rhdh-chart repo, the lightspeed image fields are simple strings in the values file:

rhdh-chart/charts/backstage/values.yaml

Lines 150 to 153 in 3275bcf

	initContainer:
	name: lightspeed-rag-init
	# -- Full image reference for the Lightspeed RAG bootstrap init container. Override for disconnected environments.
	image: quay.io/redhat-ai-dev/rag-content:release-1.9-lls-0.5.0-642c567fe10a62b5ff711654306b72912f341e05

But in the downstream chart, they are maps (note that the tag/digest is missing as well):

    initContainer:
      name: lightspeed-rag-init
      # -- Full image reference for the Lightspeed RAG bootstrap init container. Override for disconnected environments.
      image:
        registry: quay.io
        repository: rhdh/rhdh-rag-content-rhel9@sha256
        # tag is set to digest via prepare.sh script
        # tag: "${RAG_CONTENT_DIGEST}"

        tag: ""

Which issue(s) does this PR fix or relate to

Fixes https://redhat.atlassian.net/browse/RHDHBUGS-3091

How to test changes / Special notes to the reviewer

Render the backstage chart against the values file mentioned in https://redhat.atlassian.net/browse/RHDHBUGS-3091

Checklist

• For each Chart updated, version bumped in the corresponding Chart.yaml according to Semantic Versioning.
• For each Chart updated, variables are documented in the values.yaml and added to the corresponding README.md. The pre-commit utility can be used to generate the necessary content. Run pre-commit run --all-files to run the hooks and then push any resulting changes. The pre-commit Workflow will enforce this and warn you if needed.
• JSON Schema template updated and re-generated the raw schema via the pre-commit hook.
• Tests pass using the Chart Testing tool and the ct lint command.
• If you updated the orchestrator-infra chart, make sure the versions of the Knative CRDs are aligned with the versions of the CRDs installed by the OpenShift Serverless operators declared in the values.yaml file. See Installing Knative Eventing and Knative Serving CRDs for more details.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[rm3l]

/cc @Jdubrick

[Jdubrick]

lgtm