Fix PrivateLink/Private Service Connect import

[tbroden84]

WHY are these changes introduced?

When importing PrivateLink or VPC Connect resource, instance_id (required) and sleep/timeout (optional) arguments are never set. Making Terraform destroy and re-create the resource every time, due to instance_id also use ForceNew behaviour.

Reference: https://github.com/cloudamqp/terraform-provider-cloudamqp/issues/249

WHAT is this pull request doing?

• Set instance_id when no value set, just default 0 (null).
• Set sleep and timeout when no value set, just default 0 (null).
• Update docs with CloudAMQP identifier and PrivateLink identifier information.

HOW can this pull request be tested?

Import PrivateLink or VPC Connect resource.

[tbroden84]

Checked all other resources too and only these three resources fails to set the necessary instance_id.