Problem:
If you use the bot flag as an IP user or as a user without bot permissions, you get a generic 403 "rest-write-denied" error. This is not helpful to debug the underlying cause of the error.
@connorshea says: This should 1) probably be documented in the error possibilities in the OpenAPI spec, and 2) should probably have a more specific error case? I only figured this out by looking through the Wikibase repo to find the logic that triggered this error.

Example:

Acceptance criteria: