feat: add incident list command

Description

The first MR in the series of adding incident-related functionality to GitLab CLI. (TBD LINK TO THE EPIC WITH DESCRIPTION)

Adds a new incident list command to display a list of incidents. Returns the same results as issue list --issue-type=incident.

An incident is an issue with issue_type=incident. They share most of functionality, but incidents have some extra features.

• Reuses most of the issue list functionality
• Uses "incidents" in the help and docs
• Doesn't define --issue-type flag for incidents

Related Issues

Resolves #1156 (closed)

Contributes to #1155 (closed)

How has this been tested?

1. Run make build from the CLI app directory
2. Run /Users/vtatarintev/Developer/GitLab/cli/bin/glab incident list from the test repo

Screenshots (if appropriate):

incident list	issue list --issue-type=incident	incident --help	incident list --help

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)