* add feature flag
* puts search permission filtering behind a feature flag
* fixes issue with doc match id. When the match is for an in-memory index, the internal id is a string (this is what we expected). However, when its a file-based index, the internal id is a binary encoded int64 that point to something internally. So to get the id, we need to use ExternalID() instead of relying on the indexInternalID to be the correct format.
* adds debug log
* update comment
* formatting