rn,flags: add ability to override resolution using a flag

Also, use the configured resolution to set it as the max received frame size.

react/features/base/config/middleware.js

@@ -3,6 +3,7 @@
 import { jitsiLocalStorage } from 'js-utils';
 
 import { APP_WILL_MOUNT } from '../app';
+import { getFeatureFlag } from '../flags/functions';
 import { addKnownDomains } from '../known-domains';
 import { MiddlewareRegistry } from '../redux';
 import { parseURIString } from '../util';
@@ -107,6 +108,12 @@ function _setConfig({ dispatch, getState }, next, action) {
         config.p2p = { enabled: !settings.disableP2P };
     }
 
+    const resolutionFlag = getFeatureFlag(state, 'resolution');
+
+    if (typeof resolutionFlag !== 'undefined') {
+        config.resolution = resolutionFlag;
+    }
+
     dispatch({
         type: _UPDATE_CONFIG,
         config