feat: add openapi-mode config (#1881)

* openapi-mode="follow-acl"(default): follows access control for the
JWT role.
* openapi-mode="ignore-acl": ignores access control for the JWT role.
* openapi-mode="disabled": disables OpenAPI output, the root endpoint
replies with 404 Not Found.

src/PostgREST/CLI.hs

@@ -192,6 +192,10 @@ exampleConfigFile =
       |## when none is provided, 660 is applied by default
       |# server-unix-socket-mode = "660"
       |
+      |## determine if swagger output should follow or ignore ACL constraints or be disabled entirely
+      |## admitted values: follow-acl, ignore-acl, disabled
+      |openapi-mode = "follow-acl"
+      |
       |## base url for swagger output
       |openapi-server-proxy-uri = ""
       |