Feature Request : Incoming webhook to all teams with team and channel specified in payload?

You will need to create a webhook for each team, but you should be able to post to any channel on the team with the webhook.

There's instructions on how to override the channel in the Addtional Notes section of our incoming webhook documentation.

You can override the channel specified in the webhook definition by specifying a channel parameter in your payload. For example, you might have a single webhook created for Town Square, but you can use payload={"channel": "off-topic", "text": "Hello, this is some text."} to send a message to the Off-Topic channel using the same webhook URL. If an @ symbol followed by a username is specified, then the message will be sent to that user's direct message channel