refactor(api): convert bot accounts through the admin user edit endpoint (#39355)

Follow-up to https://github.com/go-gitea/gitea/pull/38966. Replaces the
unreleased `POST /admin/users/{username}/convert-type` endpoint with a
`type` field on `PATCH /admin/users/{username}`.

routers/api/v1/swagger/options.go

@@ -59,9 +59,6 @@ type swaggerParameterBodies struct {
 	// in:body
 	RenameUserOption api.RenameUserOption
 
-	// in:body
-	ConvertUserTypeOption api.ConvertUserTypeOption
-
 	// in:body
 	CreateLabelOption api.CreateLabelOption
 	// in:body