[FTS] Flag FTS indexes that are manually modified by bleve commandline tools

There are three bleve commandline tools that are capable of modifying indexes on disk. We warn users not to use these tools and that they are capable of corrupting an index. However, to rule out accidental user damage to indexes in future support cases, please modify the bleve commandline tools to mark a hidden flag that support can use to identify potentially corrupted index files.

cbft-bleve bulk - bulk loads from newline delimited JSON files

cbft-bleve create - creates a new index

cbft-bleve index - adds the files to the index