Error when trying to update notification channel associated with private Slack channel

[akahenry]

When trying to update a notification channel associated with a private Slack channel, I get the following error:

{"errors":[{"reason":"Invalid request","message":"A Slack private channel can not be set to public and vice-versa. No privateChannel definition is equivalent to false."}]}

My understanding is that, somehow, this notification channel got created without Sysdig knowing that it refers to a Slack private channel.

When trying to update this notification channel (which ends up sending a PUT request to Sysdig API), we get the above error.

How to reproduce

1. Create a Slack notification channel through the UI associating it with a private Slack channel
2. Import this resource to a local Terraform state
3. Update the Terraform resource and try to apply it

[akahenry]

I created this PR as an attempt to fix this issue.

[dbonf]

closing this after releasing the new version that also includes the support for slack private channels