Restrict permissions to create an incident to Reporter and up

What does this MR do?

This MR

• Elevates the permission from Guest+ to Reporter+ to create an incident
• Hides the Incident issue type for Guests (and its help popup) when creating an issue
• Hides the Incident issue type for Guests when updating an issue with issue type Issue
• Shows the Incident issue type for Guests when updating an issue with issue type Incident and authored by them
• Removes all (but one) RuboCop offenses from issue form feature specs
• Hides Create Incident button for Guests on Monitor > Incidents
• Based on !73823 (merged)

Contributes to #336624 (closed).

MR Roadmap

1. Move helper methods related to issue types into a helper module
2. Restrict permissions to create an incident to Reporter and up

Screenshots or Screencasts (strongly suggested)

Role	Guest	Reporter+
Monitor > Incident
Monitor > Incident Empty state
New Issue Form
Edit Issue Form
Edit Issue Form as author

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #336624 (closed)