Memebrships: Refactor Store interface

Use unified memberships table.
Add few internal API endpoints.

Change-Id: I80ac5a0f5c262e04d7898cca571b938a35d68d39
diff --git a/charts/auth-proxy/values.yaml b/charts/auth-proxy/values.yaml
index df26e50..78fe5e3 100644
--- a/charts/auth-proxy/values.yaml
+++ b/charts/auth-proxy/values.yaml
@@ -6,7 +6,7 @@
 upstream: bar.svc.cluster.local
 whoAmIAddr: https://accounts.example.com/sessions/whoami
 loginAddr: https://accounts-ui.example.com/login
-membershipAddr: https://memberships.p.example.com/api/user
+membershipAddr: https://memberships.p.example.com
 membershipPublicAddr: https://memberships.p.example.com
 groups: ""
 portName: http