Fix Stackdriver optional arugments assignments

[tbroden84]

Previous fix: 4c7b852 to correct the optional arguments queue/vhost by converting into JSON fileds. Introduced new issues by assigning wrong values during create/update including tags: #195

New fix to make sure all allowed optional arguments can be used.

resource "cloudamqp_integration_metric" "stackdriver" {
  instance_id = cloudamqp_instance.instance.id
  name = "stackdriver"
  credentials = google_service_account_key.service_account_key.private_key
  queue_allowlist = "<queue-regex>""
  vhost_allowlist = "<vhost-regex>"
  tags = "foo=bar"
}