Add TLS cert private key secret manager item to aws-resources CF template

[cliffano]

aws-resources CF template needs to have TLS cert private key secret manager item where user can then provision the cert's private key.

Because the usage is currently optional between using AWS secrets manager vs using S3, this secrets manager resource needs to have a conditional check. i.e. only provision this if user supplies aws.certificate_key_arn property.

Have a look at ChaosMonkey condition on Stack Builder https://github.com/shinesolutions/aem-aws-stack-builder/blob/master/templates/cloudformation/apps/aem/full-set/main.yaml#L3 as an example how the condition is done on a CF template.

[cliffano]

To be included in version 3.8.0 .