PLT-1326: Enable channel posts of type join or leave not trigger unread notifications

web/react/utils/constants.jsx

@@ -118,7 +118,9 @@ export default {
     POST_LOADING: 'loading',
     POST_FAILED: 'failed',
     POST_DELETED: 'deleted',
-    POST_TYPE_JOIN_LEAVE: 'join_leave',
+    POST_TYPE_JOIN_LEAVE: 'system_join_leave',
+    SYSTEM_MESSAGE_PREFIX: 'system_',
+    SYSTEM_MESSAGE_PROFILE_IMAGE: '/static/images/logo_compact.png',
     RESERVED_TEAM_NAMES: [
         'www',
         'web',

web/react/utils/utils.jsx

@@ -1243,3 +1243,7 @@ export function getPostTerm(post) {
 export function isFeatureEnabled(feature) {
     return PreferenceStore.getPreference(Constants.Preferences.CATEGORY_ADVANCED_SETTINGS, Constants.FeatureTogglePrefix + feature.label, {value: 'false'}).value === 'true';
 }
+
+export function isSystemMessage(post) {
+    return post.type && (post.type.lastIndexOf(Constants.SYSTEM_MESSAGE_PREFIX) === 0);
+}