[lib] Factor out defaultSubscription in createPendingThread

Summary:
I might want to revist this after @Ginsu lands his related diff.

Depends on D12493

Test Plan: Flow

Reviewers: kamil, marcin, ginsu

Subscribers: tomek, ginsu

Differential Revision: https://phab.comm.dev/D12494

lib/shared/thread-utils.js

@@ -426,6 +426,11 @@ type CreatePendingThreadArgs = {
   +sourceMessageID?: string,
 };
 
+const defaultSubscription = {
+  pushNotifs: false,
+  home: false,
+};
+
 function createPendingThread({
   viewerID,
   threadType,
@@ -490,10 +495,7 @@ function createPendingThread({
     currentUser: minimallyEncodeThreadCurrentUserInfo({
       role: role.id,
       permissions: membershipPermissions,
-      subscription: {
-        pushNotifs: false,
-        home: false,
-      },
+      subscription: defaultSubscription,
       unread: false,
     }),
     repliesCount: 0,
@@ -754,10 +756,7 @@ function rawThreadInfoFromServerThreadInfo(
     currentUser = {
       role: null,
       permissions: currentUserPermissions,
-      subscription: {
-        home: false,
-        pushNotifs: false,
-      },
+      subscription: defaultSubscription,
       unread: null,
     };
   }