Add rate-limit to control delivery rate

`stream` reads data (from log file or pcap) and writes it to the output destination as fast as it can. To better match real-world systems it would useful in some scenarios to control the speed at which data is delivered to the destination. This is particularly true for protocols without delivery guarantees (UDP).

There's a TODO in the code related to this.

https://github.com/elastic/stream/blob/09126d20b9ee68b1c0ba9c561b22680eca690698/internal/command/pcap.go#L87