Allow getting and modifying unit custom names in Lua

[XHawk87]

Is your feature request related to a problem? Please describe.
This would be useful for automatically applying historical names to units in scenarios as they are constructed, as well as creating notifications about these units with improved flavour text.

Describe the solution you'd like

• Unit.name - Get the unit's custom name.
• Unit:name_set(new_name) - Set the unit's custom name.

Describe alternatives you've considered
None yet.

Additional context
Discord