route-proxy: internal names are certified by the mesh's own authority

Two name spaces, two authorities (08-connectivity §2): a public name is
certified by a public CA, an internal one by the mesh's own. step-ca now
offers that second seat as internal-acme-ca beside its existing acme-ca,
and route-proxy requires both — the server dispatches by which authority
may certify the name at all, so an .internal alias stops being plain-HTTP
only without ever asking a public CA for a name it cannot validate.

modules/step-ca/module.json

@@ -8,12 +8,20 @@
     {
       "name": "acme-ca",
       "scope": "mesh"
+    },
+    {
+      "name": "internal-acme-ca",
+      "scope": "mesh"
     }
   ],
   "serves": {
     "acme-ca": {
       "path": "/acme/acme/directory",
       "roots": "/roots.pem"
+    },
+    "internal-acme-ca": {
+      "path": "/acme/acme/directory",
+      "roots": "/roots.pem"
     }
   },
   "listens": [