Add the Ability to be Able to Configure the Logger

[BenMorganMY]

This PR allows Shoryuken to be able to configure the logger such as:

Shoryuken.logger = Appsignal::Logger.new('shoryuken')
Shoryuken.logger.formatter = Shoryuken::Logging::WithoutTimestamp.new

This provides some feature parity to Sidekiq and helps developers that are using a service like AppSignal get their logs up there.

https://docs.appsignal.com/logging/platforms/integrations/ruby.html#sidekiq-logger

[DanHenton]

Just passing by, however, I've been using a custom logger for years with no issue.

You can already configure the Shoryuken logger via the options field.

# disclaimer this is sudo code and untested...
require "logger"

class MyCustomLogger < Logger; end

custom_logger = MyCustomLogger.new("my_custom_logger")

Shoryuken.options[:logger] = custom_logger

Or in the config options hash you can pass in the custom_logger instance.

Shoryuken will now log via your custom logger where you can redefine your implementation.

[BenMorganMY]

@DanHenton I believe I began with that and wanted to take it further. I wasn't confident that Shoryuken would stick with the configuration that was set via the options. I wanted a first class option so that the logger never accidentally goes to the default log.

I also needed a log that would be compatible with AppSignal for usage.