* adds new flag `-y` prompting for user confirmation before removal
* Modified existing integration tests to work with the fix#2349.
* Added tests for checking user confirmation, updated the test cases use sub-shell with `|`
* Updated the reference docs for rm sub-command
incorporated changes by @dgageot, @jeanlaurent and @nathanleclaire
Signed-off-by: Anil Belur <askb23@gmail.com>
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