Open a silent incident

[b0n54i]

Feature Description

Add an option in the modal of the /hellper_incident command so that an incident is opened silently.

A silent incident is characterized by having a private channel and not notifying the main channel of incident when it opens.

Problem

There are some incidents that the entire organization should not be to know, for example, security incidents. That said, in such cases it is necessary to carry out the entire process of opening the incident manually, including its insertion in the databases.

[tiagotor]

@NFavareto this PR will be merged? If not, we can close it? We are working in repository maintence and we need a return here.