Disable automatic creation of pacticipants so IaC doesn't need to import auto-created ressources

[timvahlbrock]

The Pact Broker creates pacticipants automatically when a contract including them is pushed. When using the Pact Terraform Provider (or comparable IaC Tools) this is really annoying, because every Pacticipant created by the Broker needs to be explicitly imported into Terraform's management. It would be really nice if it was possible to configure the broker to disable this "auto-create" behavior for when IaC is used. If a consumer is trying to add a contract that does contain not yet existent pacticipants the contract would be refused.