This patch moves the history subcommand from the command to session command.
I think it makes more sense to have it there because as the command usage
suggests, it should be used to manage custom LLDB commands.
However, history is essentially tied to a debugging session and holds
all the commands (not specifically custom ones).
This also makes it more discoverable by adding an alias for it (mimicking the shell builtin).
Signed-off-by: Med Ismail Bennani <firstname.lastname@example.org>