Service desk issues can be edited but should not.

Summary

Since service desk contents are part of email communication, the issues' contents and comments should not be editable.

Steps to reproduce

Use service desk, edit a submitted issue or a comment on it.

Example Project

What is the current bug behavior?

Edits are possible.

What is the expected correct behavior?

Edits should not be possible since they falsify the actual email communication history.

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

Results of GitLab application Check

Possible fixes

Make posted comments and the issue text of service desk issues readonly.