Explain limitations of the operator-generated key

[lin-crl]

Jianwei Lin (lin-crl) commented:

Title

Improve Operator doc

Description

State the limitation of Operator generated key, which is only be valid within the k8s cluster because of the scope of trust. For applications outside of kubernetes cluster to connect to CRDB created by Operator, customers need to use custom ca. And add a link to https://www.cockroachlabs.com/docs/stable/secure-cockroachdb-kubernetes.html#use-a-custom-ca

Outline

Expected Audience

k8s Operator users, Infra Engineers, etc

Jira Issue: DOC-2355