Tested as part of D26090, which should land after this but I couldn't find a way to stack then without arc wanting to steal this diff.

Given that supporting this is basically adding $this-getUser()->getIsSystemAgent() to PhabricatorEmailAddressesSettingsPanel in isManagementPanel (similar to how it's done in D26087), I don't see why we wouldn't do this. Sure, it's rather unlikely that you'll need to change the email address after creation, but the documentation on /people/new/bot/ states that they can interact with other systems which require an email address. It's not outside the realm of possibilities that the associated email address might need to change, and requiring manually editing the database while we have a perfectly good panel for it seems just silly.

Some of these array type hints feel sketchy, but they already were unusual. I suppose this is fine. The rest certainly is.