Route for adding new application member

- domain method for creating a new application member
- ApplicationInvitations domain class
- nested form for adding a new user that holds user data, application
  permission sets, and environment roles
- Invitation service can infer invitation type based on role it's given
- new invitation email templates

tests/services/test_invitation.py

@@ -1,9 +1,15 @@
-from tests.factories import UserFactory, PortfolioFactory, PortfolioRoleFactory
+from tests.factories import (
+    ApplicationFactory,
+    ApplicationRoleFactory,
+    UserFactory,
+    PortfolioFactory,
+    PortfolioRoleFactory,
+)
 
 from atst.services.invitation import Invitation
 
 
-def test_invite_member(queue):
+def test_invite_portfolio_member(queue):
     inviter = UserFactory.create()
     new_member = UserFactory.create()
     portfolio = PortfolioFactory.create(owner=inviter)
@@ -12,3 +18,14 @@ def test_invite_member(queue):
     new_invitation = invite_service.invite()
     assert new_invitation == new_member.portfolio_invitations[0]
     assert len(queue.get_queue()) == 1
+
+
+def test_invite_application_member(queue):
+    inviter = UserFactory.create()
+    new_member = UserFactory.create()
+    application = ApplicationFactory.create()
+    member = ApplicationRoleFactory.create(user=new_member, application=application)
+    invite_service = Invitation(inviter, member, new_member.email)
+    new_invitation = invite_service.invite()
+    assert new_invitation == new_member.application_invitations[0]
+    assert len(queue.get_queue()) == 1