LPS-47341 Fix snippet processing in OpenSearch. Also, avoid processing "null" summaries returned by some indexers
LPS-47341 Certain indexers may set "content" or "title" to null which can lead to NPE
LPS-47341 Date fields should be set to "stored" explicitely, since the default is "false" which causes that e.g. field "modified" is missing from result Document hit and it leads to a ParseException in OpenSearch
LPS-47341 src format