Enrol over http only to loopback; serve the API docs to this machine

The enrolment exemption covered any *.local host, which mDNS answers with
whoever claims it; it is now localhost, 127.0.0.0/8 and ::1. /docs, /redoc
and openapi.json stay closed in production and otherwise answer only a
loopback caller unless API_DOCS_ENABLED is set, which the dev compose does,
so `fluksio serve --host 0.0.0.0` no longer hands the schema to the network.

docker/compose.dev.yml

@@ -124,6 +124,8 @@ services:
       EMAILS_FROM_EMAIL: "info@fluksio.com"
       # Test-only user seeding, needed by the Playwright suite. Dev stack only.
       PRIVATE_API_ENABLED: "true"
+      # /docs and the schema for callers through Traefik, not only loopback.
+      API_DOCS_ENABLED: "true"
 
   mailcatcher:
     image: schickling/mailcatcher