[SPARK-20888][SQL][DOCS] Document change of default setting of...

[SPARK-20888][SQL][DOCS] Document change of default setting of spark.sql.hive.caseSensitiveInferenceMode

(Link to Jira: https://issues.apache.org/jira/browse/SPARK-20888)

## What changes were proposed in this pull request?

Document change of default setting of spark.sql.hive.caseSensitiveInferenceMode configuration key from NEVER_INFO to INFER_AND_SAVE in the Spark SQL 2.1 to 2.2 migration notes.

Author: Michael Allman <michael@videoamp.com>

Closes #18112 from mallman/spark-20888-document_infer_and_save.