Add HitWidthClusterMerging algorithms in Pandora steering XML and enabling hit widths

[mattiasotgia]

Description

This PR introduces in the Pandora reconstruction chain a couple of algorithms aimed at exploiting the hit width information to improve on the 2D cluster creation.

In addition to the change in the Pandora steering XML, the flag UseHitWidths is switched to true in the pandoramodules_icarus.fcl configuration.

Requesting review to @rtriozzi and @acampani, please let me know if anyone else should be added as reviewer for this PR.

[rtriozzi]

thanks! looks as expected.

(was there any chance of introducing the width-based algos in the cosmic pass as well? if so, should we bake them in eventually? anyway, this is good to go as is imo!)

[mattiasotgia]

was there any chance of introducing the width-based algos in the cosmic pass as well?

I think introducing the same algorithms also in the slicing pass (i.e., the first Pandora cosmic pass) would be something to investigate further.

As is now, the second Pandora cosmic pass is essentially not being used for anything, since we are saving the output of the Pandora neutrino path for all slices, so I don't have strong feelings for that one, but I agree changing the first Pandora cosmic pass could be a nice improvement.