Helm chart should specify cache and max-sql-memory programmatically

The `cache` and `max-sql-memory` fields in the [Helm chart](https://github.com/cockroachdb/helm-charts/blob/master/cockroachdb/values.yaml) should use programmatic values like in the [StatefulSet configs](https://github.com/cockroachdb/cockroach/blob/master/cloud/kubernetes/bring-your-own-certs/cockroachdb-statefulset.yaml#L220).

We have been documenting a workaround to override the Helm chart by setting these to explicit values, so having this work as-is would be an improvement.

Jira issue: HELM-53

Compare the cache and max-sql-memory entries in values.yaml with the corresponding programmatic values in cockroachdb-statefulset.yaml around line 220. Confirm how the Helm chart currently renders these fields and update it so the chart works without explicit override values.

Written by the indexing model from the issue text.