fix: add default value for clusterRole name override

[nikki-quant]

Why is this pull request needed and what does it do?

This addresses a templating error by adding a default value to the chart.

A thing the maintainers of this repo likely already know but that I felt the need to check while making this PR: setting a Helm value to an empty string results in it being treated as false in if/else statements (https://helm.sh/docs/chart_template_guide/control_structures/#ifelse). So this should be a safe default.

Which issues (if any) are related?

#180

Checklist:

• I have bumped the chart version according to versioning.
• I have updated the chart changelog with all the changes that come with this pull request according to changelog.
• Any new values are backwards compatible and/or have sensible default.
• I have signed off all my commits as required by DCO.

[hagaibarel]

Thanks for the fix!