Add back in public stats API

[mrjones-plip]

originally added in #79

[mrjones-plip]

@munroebot - still need to test this in my dev environment (which is broken - I'll fix it!) but this initially look ok to you?

[munroebot]

I can test this in the test / qa environment if you don't get around to setting up your dev host.

It looks like it should work though.

[munroebot]

Output looks good, merging into prod

(.venv) ubuntu@munroebot-access-dev:~/ShopIdentifyer$ curl https://shopid-dev.synshop.net/api/public_stats
{
  "total_door_access": 156,
  "total_free": 3,
  "total_membership": 154,
  "total_need_onboarding": 0,
  "total_not_vetted": 34,
  "total_paused": 62,
  "total_vetted": 58
}