docs: Migrated the stages API from the old docs to the new docs

[OfficialJhimmy]

No description provided.

[shinde-rahul]

@OfficialJhimmy, A minor touch-up and we are good to go.

• Fix double periods in parameter descriptions.

Please check the vale errors too.

[adiati98]

@mautic/core-team I have a couple of questions here and left comments of things that I've changed. Basically, I'm trying to make this clearer and readable. Other than these, I changed all active to passive voices.

Once you review the content in this PR, and if you all agree with the changes, I'll apply them to all API sections in this docs.

---

Here's the live preview link: https://mautic-developer--253.org.readthedocs.build/en/253/rest_api/stages.html

And here's the original version as comparison: https://github.com/mautic/developer-documentation/blob/main/source/includes/_api_endpoint_stages.md

TIA! ✨