[FTS] FTS cmd-line tools need warnings

Originally from Will G (see MB-21312)...

...please modify the help that's output so that there are appropriate warnings next to the commands that need them? I'm talking about the text that users see if they do cbft-bleve --help or similar. I think it should start with a general statement saying that the tool is intended for advanced users. By the way, is there a cbft-bleve help option?

cbft-bleve count - counts the number of documents in the index

cbft-bleve dictionary - prints the term dictionary for the specified field in the index

cbft-bleve dump - dumps the contents of the index

cbft-bleve fields - lists the fields in this index

cbft-bleve mapping - prints the mapping used for this index

cbft-bleve query - queries the index

cbft-bleve registry - registry lists the bleve components compiled into this executable

Warning! Danger, Will Robinson!

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