terraform: cache: configure as Requester Pays

[delroth]

Not applied yet, will apply on 2023-11-04 (Saturday).

  # aws_s3_bucket_request_payment_configuration.cache will be created
  + resource "aws_s3_bucket_request_payment_configuration" "cache" {
      + bucket = "nix-cache"
      + id     = (known after apply)
      + payer  = "Requester"
    }

Plan: 1 to add, 0 to change, 0 to destroy.

Will merge once applied and tested to not explode, filing this PR to get any review feedback prior to applying later this week.

Fixes #277

[delroth]

Pushed.