Upload Files V2: Ability to upload multiple files in one message

[rbreeze]

Description

With V2 File uploading, Slack added the ability to upload multiple files to one message to its Python SDK. Would be great to have it here.

Slack's documentation

https://github.com/slackapi/python-slack-sdk/releases/tag/v3.19.0

[parsley42]

Hi @rbreeze - I'm retiring from being the de facto maintainer of this project; slack-go/slack needs maintainers, please email me at the address on my GitHub page if interested, thanks.