feat(config) add gravatar config object (#11509)

config.js

     // Array with avatar URL prefixes that need to use CORS.
     // corsAvatarURLs: [ 'https://www.gravatar.com/avatar/' ],
 
-    // Base URL for a Gravatar-compatible service. Defaults to libravatar.
-    // gravatarBaseURL: 'https://seccdn.libravatar.org/avatar/',
+    // Base URL for a Gravatar-compatible service. Defaults to Gravatar.
+    // DEPRECATED! Use `gravatar.baseUrl` instead.
+    // gravatarBaseURL: 'https://www.gravatar.com/avatar/',
+
+    // Setup for Gravatar-compatible services.
+    // gravatar: {
+    //     // Defaults to Gravatar.
+    //     baseUrl: 'https://www.gravatar.com/avatar/',
+    //     // True if Gravatar should be disabled.
+    //     disabled: false
+    // },
 
     // App name to be displayed in the invitation email subject, as an alternative to
     // interfaceConfig.APP_NAME.

react/features/base/config/configWhitelist.js

     'gatherStats',
     'giphy',
     'googleApiApplicationClientID',
+    'gravatar.disabled',
     'hiddenPremeetingButtons',
     'hideConferenceSubject',
     'hideDisplayName',

react/features/base/participants/functions.js

         return participant && participant.avatarURL ? participant.avatarURL : null;
     },
     (participant, store) => {
-        if (participant && participant.email) {
-            // TODO: remove once libravatar has deployed their new scaled up infra. -saghul
-            const gravatarBaseURL
-                = store.getState()['features/base/config'].gravatarBaseURL ?? GRAVATAR_BASE_URL;
+        const config = store.getState()['features/base/config'];
+        const isGravatarDisabled = config.gravatar?.disabled;
+
+        if (participant && participant.email && !isGravatarDisabled) {
+            const gravatarBaseURL = config.gravatar?.baseUrl
+                || config.gravatarBaseURL
+                || GRAVATAR_BASE_URL;
 
             return getGravatarURL(participant.email, gravatarBaseURL);
         }