docs(ci): document release smoke testing process

[gustavolira]

Summary

• Adds .ci/release-smoke-testing.md documenting how to run the CI test suite against productized RHDH images for release validation
• Covers: overriding image variables, updating values files, running additional test suites, testing on custom clusters, and the [skip-build] tip
• Based on the process used in [TESTING DO NOT MERGE] Test rhdh 1.9 211 #4431

Jira

https://redhat.atlassian.net/browse/RHIDP-8640

Test plan

• Review the document for accuracy against the actual PR [TESTING DO NOT MERGE] Test rhdh 1.9 211 #4431 changes
• Confirm file paths and variable names match the current codebase

🤖 Generated with Claude Code

[github-actions]

The container image build workflow finished with status: cancelled.

[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

[github-actions]

Image was built and published successfully. It is available at:

• quay.io/rhdh-community/rhdh:pr-4449
• quay.io/rhdh-community/rhdh:pr-4449-d22b5949

[josephca]

/lgtm
/approve

[zdrapela]

@gustavolira @josephca
Have you guys tried #4355? Did it work for you, or do you have any ideas for improvement? I believe it's a superior way of triggering jobs with the option to override the image, rather than opening a PR with specific values.

[zdrapela]

These steps are completely redundant. They are basically placeholders which are getting overriden by helm upgrade -i which uses this function for params:

rhdh/.ci/pipelines/lib/helm.sh

Lines 214 to 225 in 30f6369

	helm::get_image_params() {
	local params=""
	# Add image repository
	params+="--set upstream.backstage.image.repository=${QUAY_REPO} "
	# Add image tag
	params+="--set upstream.backstage.image.tag=${TAG_NAME} "
	echo "${params}"
	return 0
	}

It's actually pretty misleading, and we should replace them or delete them from the value files.

[zdrapela]

PR to remove them as a proof: #4457