Does gsutil support custom plugin

I have a use case when user uploads files using gsutil to a particular bucket ``` gsutil cp -r directory gs://bucket/path ```, i would like it to send an additional http post information to a third party website once the upload is completed. This is to trigger the subsequent job. Is it better to write a plugin instead of forking gsutil and customize the code directly? Any guideline to write gsutil plugin?

Start by reviewing the gsutil plugin and extension guidance, if any, and the upload flow for `gsutil cp -r directory gs://bucket/path`. Determine whether a plugin can send an HTTP POST after completion or whether the request is asking for new plugin support; done means documenting the supported approach and guidelines.

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