chore(ci): Add Snyk scan for Backstage with Orchestrator

[Fortune-Ndlovu]

Description of the change

• Refactors Snyk scan workflow to use a matrix-driven approach for configuring Helm chart render options.
• Each scan variant is defined with a name, path, and cliArgs, removing hardcoded conditionals from the job logic.
• Adds backstage-orchestrator scan using --set flags to enable Orchestrator at scan time only.
• Ensures all Snyk project names are consistently prefixed with redhat-developer/rhdh-chart/*.

Existing or Associated Issue(s)

https://issues.redhat.com/browse/RHIDP-6631

Additional Information

Checklist

• Chart version bumped in Chart.yaml according to semver.
• Variables are documented in the values.yaml and added to the README.md. The pre-commit utility can be used to generate the necessary content. Use pre-commit run -a to apply changes.
• JSON Schema template updated and re-generated the raw schema via pre-commit hook.
• List tests pass for Chart using the Chart Testing tool and the ct lint command.

[rm3l]

Also, as discussed alrady, could you temporarily add a pull_request trigger, so that we can see this Workflow in action in this PR? I guess the PR will likely not have access to the repo secrets, but that should be fine. I just want to see how the template rendering steps behave here.

[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]

/lgtm