Using std::string_view

[methylDragon]

The established pattern in warehouse_ros is to pass const std::string& to prevent a copy.

However this prevents use of the more modern std::string_view in code building on top of warehouse_ros, forcing them to copy into an std::string just to call into methods of warehouse_ros (when a copy would've been prevented in the first place!).

Since we moved to C++17 in Galactic, which supports std::string_view, we probably should move to using std::string_view instead.

I'm not sure if there are any issues with just doing a sweeping find and replace though, for anyone depending on warehouse_ros?