cli: add option for changing save path
Save path is a directory where config change (delta) files are stored.
Having a custom individual save dir can be used to prevent two (or more)
"uci" cli callers (e.g. bash scripts) from commiting each other changes.
In the following example:
App0 App1
---- ----
uci set system.@system[0].timezone=UTC
uci set system.@system[0].hostname=OpenWrt
uci commit system
App1 would unintentionally commit changes made by App0. This can be
avoided by at least 1 "uci" cli user specifying a custom -t option.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>