Update ChatGPT Ads Ad Group

Changes the name, bid, bid strategy or context hints of an existing ChatGPT Ads ad group.

Context hints are what decides which ChatGPT conversations the ads can match, so this is the main relevance lever on the platform. Write them as short natural sentences describing the product, the use case or the need, in the language the buyers actually chat in: "lightweight trail running shoes for rocky terrain" works, "shoes" does not, and "customers in California" belongs in country targeting instead. Up to 2000 per ad group; they are not exact-match keywords and they do not replace country or platform targeting. `hints_mode`: `add` appends to what is already there (the default, and the safe one), `replace` swaps the whole list, `remove` deletes the ones you pass, `clear` empties it. OpenAI's own field is replace-only, so a bare `replace` with two hints would silently delete the rest; the merge happens here. `max_bid` is in the account currency and is checked against the parent campaign's real daily budget plus a sanity ceiling that catches a decimal slip; a deliberate high bid passes with `allow_high_bid=true`. `strategy`: fixed_bid | maximize_clicks | maximize_conversions. Switching to a maximize strategy drops the manual bid because OpenAI requires it to be absent there. Bid settings not passed, including audience bid multipliers, are preserved, not cleared. confirm=false returns a dry run.