Disallow Guest authors to close Incidents

Summary

Steps to reproduce

• Create a project as Owner (or Admin/Maintainer)
• Invite user as a Guest
• Guest creates an Issue - they cannot create Incident since #336624 (closed)
• Owner changes Issue Type from Issue to Incident
• Guest visits the (now) Incident and sees Close Incident

What is the current bug behavior?

Guest author is able to close incidents.

What is the expected correct behavior?

Guest author should not be able to close incidents.

Relevant logs and/or screenshots

Proposal

Create a new permission close_incident

Use it in frontend and backend instead of close_issue

Tweak existing policies update_issue and reopen_issue

See #345394 (comment 940492790)