Inherit viewability of incidents from issues

What does this MR do?

In this MR:

• Drops read_incidents, instead using read_issue directly as incidents should be readable with the same rules as standard issues
• Ensures the 'Operations' menu shows up for the people it's supposed to (including a few permissions that were missed)

Related issue: https://gitlab.com/gitlab-org/gitlab/-/issues/232750

Screenshots

Note that the "hovered-over" blue incident in the owner view is a confidential issue. This is in a public project.

Menu - anon user	Incidents - anon user	Menu - owner	Incidents - owner

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done