Replace incorrect use of getStatusFromCommandResult in ShardServerCatalogCacheLoader

The shard chunk loader is using getStatusFromCommandResult to parse command responses. However, getStatusFromCommandResult does not parse writeErrors and should not be used to parse write command response. The code should be moved off of getStatusFromCommandResult and instead use the BatchedCommandResponse::toStatus() function.

Additionally, add a note to the getStatusFromCommandResult function comment that it cannot be used for write command responses.