[TF2] [Feature Request] Add a cvar allowing players to equip conflicting items

[KimmyTF2]

This is mostly related to issues and suggestions like https://github.com/ValveSoftware/Source-1-Games/issues/4055, https://github.com/ValveSoftware/Source-1-Games/issues/4102, https://github.com/ValveSoftware/Source-1-Games/issues/4314, and https://github.com/ValveSoftware/Source-1-Games/issues/4660. Many combinations of hats/misc items are not intended to be worn at the same time, but players like to create their own abominations or wear multiple Unusual items that normally are not possible. While equipping conflicting items is a bug and eventually should be fixed (items with multiple equip regions using "equip_region" instead of "equip_regions" and a method with +quickswitch command were already fixed just to be reverted shortly after), a cvar for community servers could allow players to mess with cosmetics as much as they want without messing with any exploits, while on official servers this could be fixed for good this time. For example a cvar tf_allow_conflicting_items 0/1 disabling equip region restrictions.