shared: shell: Only omit consecutive duplicate history lines.

shared: shell: Only omit consecutive duplicate history lines.

Change rl_handler to append duplicate history, as long as it isn't
identical to the last line. It prevents consecutive duplicates while
still having an accurate overview of the most recent commands used,
mimicking most modern shells.

This addresses my only major gripe with bluetoothctl: pressing UP does
not retrieve the last typed command when it is a duplicate of something
else written (much) earlier in the history. It is especially noticeable
when needing the same command repeatedly.

Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>