Add `RedisConfirmationStrategy` for using HiTL with Hayhooks and Open WebUI

[mpangrazzi]

We recently created an HiTL demo using Redis, Open WebUI and haystack-experimental. It uses a custom RedisConfirmationStrategy which in turns uses Redis blocking commands like BLPOP for non-blocking approval wait.

We may want to add this custom confirmation strategy to haystack-experimental. It will probably need to be refactored for better flexibility.