Upload a conversion CSV

Let the user upload a conversion CSV for an offline conversion upload.

For the CSV behind draft_upload_call_conversions or draft_upload_enhanced_conversions_for_leads when the file is not on the machine running AdLoop, as on AdLoop Cloud. Apps that show AdLoop's cards display an upload card where the user drops the .csv file; the card then posts the upload id into the chat. Other apps on AdLoop Cloud get an upload link for the user (or a coding agent, with curl). The file holds personal data (phone numbers, emails), so it is kept for two hours at most and deleted as soon as a draft has read it. Returns the CSV uploads waiting to be used and how to add one.

Google Ads API: https://developers.google.com/google-ads/api/docs/start