Create Backward compatibility tests for kNN to make Lucene upgrade does not break the ODFE version upgrade

[vamshin]

We have noticed when Elasticsearch upgrades to the latest version of Lucene, to maintain backward compatibility it allows to write using latest codec and allows to read old indices with the corresponding old Codes. We need to have tests to ensure that the above behavior is working as expected similar to https://github.com/apache/lucene-solr/blob/master/lucene/backward-codecs/src/test/org/apache/lucene/index/TestBackwardsCompatibility.java