Add logback extension module for Sentinel logger SPI

[sczyh30]

Issue Description

Umbrella issue: #1295

Type: feature request

Describe what happened (or what feature you want)

Add logback extension module (sentinel-logging-extension-logback in sentinel-extension) for Sentinel logger SPI. We may refer to the logback sample and #757 (comment)

Contributions are welcomed!

[zhaoyuguang]

I wanna try to finish it

[jasonjoo2010]

I wanna try to finish it

Good to hear that.
And please pay attention to recent changes which will be merged: #1355
You may rebase to the newest code before submitting.

[sczyh30]

As it's rare to use the loggers of the logging framework directly (without slf4j), I think this issue is no longer necessary and can be closed. Please reopen the issue if needed :)

Thanks for your contribution! @zhaoyuguang