followUser method
Implementation
void followUser(String userId) async {
final result = await friendshipManager.followUser(userIDList: [userId]);
const success = 0;
if (result.code == success) {
final Set<String> followingList = Set.from(state.followingList.value);
followingList.add(userId);
state.followingList.value = followingList;
getFansNumber();
}
}