keycloak: provide oidc-client, one mesh-made client per consumer

A module that logs people in through Keycloak had to be given a client by
hand, with its secret copied into the consumer's environment. As a provision
the mesh derives the client id (the consumer's identity, mesh_<node>_<module>)
and mints its secret, and delivers both ends: keycloak creates exactly that
confidential client, the consumer names it through ${bound:oidc-client:as}.

The consumer says where its browser comes back to (`callback`) and which
endpoint it is reached on (`label`/`endpoint`), so the redirect is built from
the same names the mesh composes for its route. keycloak serves the issuer and
the endpoint paths under it; the issuer is the one value an assignment sets,
and the realm is read out of it, so consumer and client cannot disagree.

Only what the mesh made is touched: its clients carry mesh.provisioned=true;
a client of the same id without the mark is refused, never adopted, updated
or deleted. The runtime now gets the admin password as a file, which its
tools also needed and never had.

modules/keycloak/tsconfig.json

@@ -8,5 +8,5 @@
     "skipLibCheck": true,
     "noEmit": true
   },
-  "include": ["client.ts", "index.ts", "tools/index.ts"]
+  "include": ["client.ts", "oidc.ts", "index.ts", "provisioner/index.ts", "tools/index.ts"]
 }