Upload an image or video to PinBridge and get an asset_id for create_pin.
Use when the media was generated in this session or Pinterest cannot
fetch it from a public URL; otherwise pass image_url to create_pin
directly. Provide exactly one of content_base64 or source_url. Videos
must be uploaded assets.
Returns id (use as asset_id), public_url, asset_type, content_type,
size_bytes, created_at. Files are capped at 200 MB (plans cap lower).
Fails with payment_required on plans without uploaded_media_assets
(see get_billing_status), validation_error for unsupported media, and
invalid_image when the file is truncated or corrupted (re-encode the
exact original bytes; never retype base64 by hand).
ConnectorAPI key