KRaft support in FetchRequestDownConversionConfigTest

The following tests in FetchRequestDownConversionConfigTest in core/src/test/scala/unit/kafka/server/FetchRequestDownConversionConfigTest.scala need to be updated to support KRaft

100 : def testV1FetchWithDownConversionDisabled(): Unit = {

117 : def testLatestFetchWithDownConversionDisabled(): Unit = {

134 : def testV12WithDownConversionDisabled(): Unit = {

Scanned 271 lines. Found 2 KRaft tests out of 5 tests