Create a Performance Max non-retail asset group with all required assets in one bulk mutate

Steps

1. Create the campaign and budget resources first, then prepare a single bulk mutate request containing the AssetGroup plus every AssetGroupAsset link.
2. Include the minimum required text assets: at least 3 headlines (max 30 chars each), 1 long headline (max 90 chars), at least 3 descriptions (max 90 chars each), and 1 business name.
3. Include at least 1 landscape image (1.91:1) and 1 square image (1:1) linked as MARKETING_IMAGE and SQUARE_MARKETING_IMAGE asset field types respectively, plus at least 1 logo image.
4. If brand guidelines are enabled on the campaign, attach BUSINESS_NAME, LANDSCAPE_LOGO, and LOGO assets as CampaignAsset objects rather than AssetGroupAsset objects.
5. Submit the entire AssetGroup + AssetGroupAsset set in one GoogleAdsService.MutateAsync call; the API will reject the request if the asset group and its minimum assets are not created together.
6. Check the partial_failure_error field in the response and inspect asset_group_asset errors separately, as asset validation errors surface there rather than at the top-level campaign error.