Refactors the incident template
For https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/12681
This refactors some of the incident review template, summary of changes:
- Removes comments about things that are now automated with woodhouse
- Moves note about redacting public content to the bottom of the issue, so the Summary is the focus
- Improves instructions for corrective actions
- Removes "5-whys"
- Removes incident review stakeholder section, as we aren't using this section and can bring in people if we go through review