This change adds a new menu containing management commands for connected

services (which is currently HostingServiceAccount). For now, this

only contains a single item, "Edit Credentials", which pops up a dialog

similar to the wizard to let people enter new credentials for the

account (which is already a much improved experience over what they had

to do previously, which was enter the repository form and edit the

credentials inline in there). This menu is currently empty (and

therefore hidden) for GitHub accounts which use an app installation,

since there's no credentials to edit there.

Ran unit tests.
Edited credentials for a linked Forgejo account.