[FEATURE REQ] Document subscriptions

[kwin]

Please describe the feature.

The extractor in version 6.0.2 generates subscriptions below /subscriptions/<uuid>, however those are not documented in https://azure.github.io/apiops/apiops/3-apimTools/apiops-2-1-tools-extractor.html#artifacts.
Also are those supported in environment specific overrides?

[github-actions]

  Thank you for opening this issue! Please be patient while we will look into it and get back to you as this is an open source project. In the meantime make sure you take a look at the [closed issues](https://github.com/Azure/apiops/issues?q=is%3Aissue+is%3Aclosed) in case your question has already been answered. Don't forget to provide any additional information if needed (e.g. scrubbed logs, detailed feature requests,etc.).
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