IPIP: Add "delete provider" to Content Routing HTTP API

The idea here is to let the publisher manage the lifecycle of provider records. This may be simple TTL eviction or something more sophisticated like deduplication of records. Idempotency may become more important here since we are manually managing resource lifecycle. This is likely a use case for network indexers, but we haven't fleshed out the details yet, likely @ischasny will add once we know more.