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.

test/io-tests/configs/expected/boolean-string.config

@@ -17,6 +17,7 @@ jwt-role-claim-key = ".\"role\""
 jwt-secret = ""
 jwt-secret-is-base64 = true
 log-level = "error"
+openapi-mode = "follow-acl"
 openapi-server-proxy-uri = ""
 raw-media-types = ""
 server-host = "!4"