Editors cannot assign themselves as Reviewers

Is your feature request related to a problem? Please describe.
Currently editors are not considered valid reviewer candidates for an article they are assigned as an editor to.

Describe the solution you'd like
As an editor, I can assign myself as a peer reviewer, even to a paper I'm editing
As an editor I can assign fellow editors / section editors to a paper as peer reviewers (already possible?)
As an editor, when I assign myself or a fellow editor/section editor, I see a warning as this can be considered a peer review malpractice in many cases (use a confirmable form perhaps?)

Describe alternatives you've considered
It should be consdiered that it is not appropriate for an editor to also be a reviewer for an article. Should Janeway be opinionated about this or should it allow this?

No files, tests, or entry points are named. First clarify whether editors should be allowed to review assigned papers and what warning or confirmation behavior is required, then locate the reviewer-candidate and assignment flow. Done should include an agreed policy and tests covering editor and fellow-editor assignments.