Add tags to N1QL statements to allow redaction at log collection time

We would like to be able to collect completed and prepared requests as part of cbcollect_info (with select * from system:completed_requests and select * from system:prepareds respectively).

There is a potential privacy issue if we include the full N1QL Statement (keys, field names may include personal information).

We could avoid this by simply not selecting the Statement field, but this poses a supportability issue (we would not necessarily know which query to investigate).

A solution would be to add tags to the statement field so that they can be caught by the log redaction process (to keep it simple, tag the entire field rather than trying to tag the non-keywords).