monitor: Add option to force output color

monitor: Add option to force output color

Sometimes we want to force output color even when stdout is not a
terminal, for example when piping the output to a filter script and then
piping it further to a pager which can display colors.

This patch provides a general option to force whether color is on or off
(always and never), or leave btmon to decide (auto).

Reviewed-by: Daniel Winkler <danielwinkler@google.com>
Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>