Support for auto-gennerate client_id and client_secret for API gateway subscription

[hkantare]

No description provided.

[kavya498]

resource "ibm_api_gateway_endpoint_subscription" "subs" {
artifact_id = data.ibm_api_gateway.endpoint.endpoints[0].endpoint_id
client_id = var.client_id
name = var.subscription_name
type = var.subscription_type
client_secret = var.secret
}
support the auto-generation feature of parameters in API Gateway subscription resource when the user doesn't provide client_id or client_secret values in the payload.
i.e it must be able to support

resource "ibm_api_gateway_endpoint_subscription" "subs" {
artifact_id = data.ibm_api_gateway.endpoint.endpoints[0].endpoint_id
name = var.subscription_name
type = var.subscription_type
generate_secret= true
}

[hkantare]

Duplicate of #1375