Show ignored confs & hide warnings for conf already set in SparkSession.builder.getOrCreate

Currently, SparkSession.builder.getOrCreate() is too noisy even when duplicate configurations are set. And users cannot tell which configurations are to fix. See the example below:

./bin/spark-shell --conf spark.abc=abc

import org.apache.spark.sql.SparkSession
spark.sparkContext.setLogLevel("DEBUG")
SparkSession.builder.config("spark.abc", "abc").getOrCreate

...
21:12:40.601 [main] WARN  org.apache.spark.sql.SparkSession - Using an existing SparkSession; some spark core configurations may not take effect.

This is strait forward when there are few configurations but it is difficult for users to figure out when there are too many configurations especially when these configurations are defined in property files like spark-default.conf that is sometimes maintained separately by system admins.

See also https://github.com/apache/spark/pull/34757#discussion_r769248275