Handle highway=construction

I started working on a neighborhood that is bordered by a road currently in construction/renovation: https://www.openstreetmap.org/way/1102390702

The road itself only had `highway=construction`, to which I've added `construction=secondary` to match what the [Wiki](https://wiki.openstreetmap.org/wiki/Tag:highway=construction) recommend.

Because of the more or less temporary nature of road work, compared to the long span work done through LTN, I think that LTN should include those roads by default. If we want to still ignore them, we can put a modal filter on them.

If present, it should use the value present in the `construction` tag, in that case treat that road as `highway=secondary`.

What do you think ?