[lib] fetchLedFarcasterChannels method

Summary:
similar to fetchFollowedFarcasterChannels, except we filter out channels that the user does not lead

Depends on D13293

Test Plan:
https://gist.github.com/vdhanan/fdc48cf3a29f0394ec5646f7c728cefa

confirmed that the new method returned all the channels led by that user and that the existing method returned the same results as before

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13295

lib/types/farcaster-types.js

@@ -33,5 +33,9 @@ export type NeynarChannel = {
   +id: string,
   +name: string,
   +follower_count: number,
+  +lead: {
+    +fid: number,
+    ...
+  },
   ...
 };

lib/utils/neynar-client.js

@@ -169,6 +169,13 @@ class NeynarClient {
     return this.fetchFollowedFarcasterChannelsWithFilter(fid, () => true);
   }
 
+  fetchLedFarcasterChannels(fid: string): Promise<NeynarChannel[]> {
+    return this.fetchFollowedFarcasterChannelsWithFilter(
+      fid,
+      channel => channel.lead.fid === parseInt(fid),
+    );
+  }
+
   async fetchFarcasterChannelByName(
     channelName: string,
   ): Promise<?NeynarChannel> {