New output plugin: logstash-output-qingstor

Hi:
I would like to contribute https://github.com/Tacinight/logstash-output-qingstor.
As mentioned in https://github.com/elastic/logstash/issues/7000, this is a twin output plugin for qingstor.

Best wishes.

Review the linked qingstor output plugin and Logstash issue #7000 first, then compare the existing contribution with Logstash's output-plugin requirements. The issue names no files or tests; done would require determining whether the external plugin is ready for inclusion and completing the repository's acceptance process.

Written by the indexing model from the issue text.