Add mbart-large-cc25, support translation finetuning (#5129)

improve unittests for finetuning, especially w.r.t testing frozen parameters
fix freeze_embeds for T5
add streamlit setup.cfg

examples/longform-qa/eli5_app.py

@@ -1,10 +1,10 @@
 import faiss
 import nlp
 import numpy as np
+import streamlit as st
 import torch
 from elasticsearch import Elasticsearch
 
-import streamlit as st
 import transformers
 from eli5_utils import (
     embed_questions_for_retrieval,