cert-manager already does this, and it's quite useful when you're using it as a subchart because you don't need to create another variable in your own values.yaml. trust-manager has defined in its schema that it doesn't accept variables not defined in the schema, so it needs to be added in the original Helm chart.

https://github.com/cert-manager/cert-manager/blob/9aa47a01ded1a47e772909f03a816f1a73680769/deploy/charts/cert-manager/values.yaml#L1458-L1465