[FEATURE] Enhance `dedup` PPL command with `keepevents` option

[ykmr1224]

Add keepevents option to dedup PPL command.
If true, keep all events, but will remove the selected field values from events after the first event containing a particular combination of values.

Syntax:
dedup ...(other params) [keepevents=<bool>]

Example:
dedup user keepevents=true

Priority: Low (Expecting lower usage)