Add a custom knowledge page

Adds a page you author yourself to the hub and indexes it into the hub's knowledge store before answering — no polling. The page is stored with origin user, which means the hub's rebuilds never overwrite or remove it. category groups the page alongside the generated ones and defaults to custom. The hub's owner can add pages, and so can anyone on the team when it is the team's shared hub; the hub needs a finished first build: a hub whose knowledge store does not exist yet — one still processing, or a draft — answers 409 KNOWLEDGE_HUB_NOT_READY, and a hub with no knowledge pages at all (one built before the pages pipeline, and a draft that was never built) answers 409 KNOWLEDGE_HUB_PAGES_UNAVAILABLE first.

Errors:

• 404 KNOWLEDGE_HUB_NOT_FOUND — No hub with that id, it was deleted, or it belongs to another team.
• 409 KNOWLEDGE_HUB_NOT_READY — The hub is still building, or its build never finished.
• 409 KNOWLEDGE_HUB_PAGES_UNAVAILABLE — The hub predates knowledge pages.
• 403 KNOWLEDGE_HUB_OWNER_ONLY — You can read this teammate's hub, but it is not your team's shared hub, so only its owner can add pages.
• 422 VALIDATION_FAILED — title or content missing or too long, or an unknown category.
• 500 UNEXPECTED_ERROR — The page was saved but could not be indexed; edit it (PATCH) to retry the indexing.
• 429 RATE_LIMITED — More than 30 knowledge-hub/campaign requests in a minute (or 1000 in a day). Knowledge hubs share the campaigns bucket.

Requires one of the following token scopes: campaigns.