controller: check for duplicate tunnel ip #1054
Description
During #1025 we hit a scenario where the activator was allocating the same tunnel IP/block for a user, which resulted in the DZD the user was connected to being unable to apply the config given to it by the controller because it was invalid with the duplicate tunnel blocks. The controller should validate against this, emit prometheus alerts if it encounters it, and not include the duplicate in the config rendered to the agent.