[terraform-ibm-secrets-manager] Expose `service_credentials_existing_serviceid_crn` and `service_credentials_parameters`

[ocofaigh]

Expose the features added in https://github.com/terraform-ibm-modules/terraform-ibm-secrets-manager-secret/releases/tag/v1.5.0 to the module and the DA

[alex-reiff]

@shemau Is there anything left to do here?