Async logging of error

EventLoopFuture+whenFailureLog.swift

import NIO
import Logging

extension EventLoopFuture {
    func whenFailureLog(
        level: Logger.Level = .error,
        _ message: @escaping @autoclosure () -> Logger.Message,
        using logger: Logger,
        errorDescriptionMetadataKey: String = "reason",
        metadata: @escaping @autoclosure () -> Logger.Metadata? = nil,
        file: String = #file, function: String = #function, line: UInt = #line
    ) {
        self.whenFailure { error in
            var logger = logger
            logger[metadataKey: errorDescriptionMetadataKey] = "\(error)"
            logger.log(level: level, message(), metadata: metadata(), file: file, function: function, line: line)
        }
    }
}