COS/KMS resources should not be provisioned when existing EN CRN is supplied

[in-1911]

When the module is used with the existing Event Noitications instance CRN, the COS and KMS parameters should be ignored and the module should not try to provision the related resources (COS instances, buckets, S2S authorizations, KMS keys)

Currently it creates all of the above even though it cannot be connected to the existing EN instance.

Affected modules

Terraform CLI and Terraform provider versions

• Terraform version:
• Provider version:

Terraform output

Debug output

Expected behavior

Actual behavior

Steps to reproduce (including links and screen captures)

1. Run terraform apply

Anything else

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[ocofaigh]

PR merged: #267