The error "spec.externalName: Invalid value" is returned when configuring the 'keycloak-db-secret' from the Red Hat Single Sign-On (RH SSO) Operator

Issue

When changing the keycloak-db-secret, one of the following messages are output in the Keycloak Custom Resource Definition (CRD):

Service "keycloak-postgresql" is invalid: spec.externalName: Invalid value: "<VALUE>": a lowercase RFC 1123 subdomain must consist of lower case alphanumeric characters, '-' or '.',  and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*').

Service "keycloak-postgresql" is invalid: spec.externalName: Invalid value: "<VALUE>": a DNS-1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')