Slack service integration API should support "confidential_note_channel" parameter
Problem to solve
In the UI interface, Slack integration service has a "Confidential note channel name" parameter. But there is no such parameter in the Slack service API, so there is no way to set this field through the API.
This issue may also be relevant to other services, like Mattermost.
Proposal
Add confidential_note_channel option to Create/Edit Slack service API. Document it.