Add ndcg and sum_gain in known ranking metrics for custom perf tagging (

#1498)

## Description

This PR adds ndcg and sum_gain in the list of known ranking metrics
columns, so it will be automatically tagged as custom performance for
whylabs.

- [x] I have reviewed the [Guidelines for Contributing](CONTRIBUTING.md)
and the [Code of Conduct](CODE_OF_CONDUCT.md).

---------

Co-authored-by: felipe207 <felipe@whylabs.ai>

python/whylogs/api/writer/whylabs.py

@@ -86,6 +86,8 @@
     "recall_k_": "mean",
     "top_rank": "mean",
     "average_precision_k_": "mean",
+    "norm_dis_cumul_gain_k_": "mean",
+    "sum_gain_k_": "mean",
 }