deprecating files.upload

[sewenthy]

We want to remind you about an upcoming date and change to the files.upload web API method that affects your app.
March 11, 2025
• Support for the files.upload API will be discontinued.
To prepare for this change, we recommend migrating away from files.upload and instead using the combination of files.getUploadURLExternal and files.completeUploadExternal. More information on how to use these two APIs together can be found on our Working with files documentation. You can also leverage Slack's SDKs to help you transition to this new way of uploading files by visiting our api.slack page.