Allow to mark API execution as failed (and don't charge them)

[shesek]

Allow services to signal that API execution has failed, which should free up the payment token and allow it to be used for another API call.

• If the X-Charge response header is set to yes, consider the request a success and mark the payment token as spent. If the X-Charge header is set to any other value (normally no), consider the request a failure and mark the payment token as usable.

• If the X-Charge response header is not specified,

  • If the --explicit-charge config option is set, consider the request a failure.

  • If the --explicit-charge config option is not set, consider the request a success if the status code is 2xx or 3xx, otherwise consider it a failure.

Freeing up the payment token means removing it from the spent table, which means we should log the execution error to a separate (new) table.