Use portfolio_role entity to display and update portfolio member info.

Previously, we were encoding the portfolio_role.user_id as part of the
form data for the portfolio admin page. This was convenient because it
allowed us to easily determine certain display attributes in the
template. Instead, we should rely on the PortfolioRole as the source of
truth for member information. This commit adds:

- Portfolio.owner_role to return the PortfolioRole of the owner
- explicitly passes the PortfolioRole IDs for the PPoC and current user
  to the template
- PortfolioRole.full_name for deriving the member name

atst/forms/portfolio_member.py

@@ -9,8 +9,8 @@ from atst.utils.localization import translate
 
 
 class PermissionsForm(BaseForm):
-    member = StringField()
-    user_id = HiddenField()
+    member_name = StringField()
+    member_id = HiddenField()
     perms_app_mgmt = SelectField(
         translate("forms.new_member.app_mgmt"),
         choices=[