feat(ClientOptions): add support for setting an initial presence (#2320)

* docs/feat(WebsocketOptions): Parse ws options presence

Allow the `presence` property in `WebsocketOptions` to be used the same way
as `ClientUser#setPresence`.

* Move presence options to top level

src/util/Constants.js

@@ -26,6 +26,7 @@ const browser = exports.browser = typeof window !== 'undefined';
  * corresponding websocket events
  * @property {number} [restTimeOffset=500] Extra time in millseconds to wait before continuing to make REST
  * requests (higher values will reduce rate-limiting errors on bad connections)
+ * @property {PresenceData} [presence] Presence data to use upon login
  * @property {WSEventType[]} [disabledEvents] An array of disabled websocket events. Events in this array will not be
  * processed, potentially resulting in performance improvements for larger bots. Only disable events you are
  * 100% certain you don't need, as many are important, but not obviously so. The safest one to disable with the
@@ -47,6 +48,7 @@ exports.DefaultOptions = {
   restWsBridgeTimeout: 5000,
   disabledEvents: [],
   restTimeOffset: 500,
+  presence: {},
 
   /**
    * WebSocket options (these are left as snake_case to match the API)