[Improvement] Enhance Request Deduplication with Generated Cache Key

[MattCCC]

Currently, the fetchff plugin only utilizes a short-lived, per-request configuration that is passed during each request. This approach does not effectively handle request deduplication, potentially leading to redundant network traffic and increased server load.

To improve the efficiency of the fetchff plugin, we need to implement a strategy that uses a generated cache key for request deduplication. This will help avoid unnecessary requests and improve response times.

Expected behavior:
If previous request to the same endpoint is in progress elsewhere, the current call should await for the call from the previous one to finish.