Allow customisation of how sabotage unit works

[XHawk87]

Is your feature request related to a problem? Please describe.
Currently, the Sabotage Unit outcome is very rigid. It does exactly 50% damage to the target unit on success, regardless of unit type or circumstances, and will kill after HP reaches exactly 1.

Describe the solution you'd like

• Move the implementation to default.lua so that it can be customised in rulesets.
• Add effects to modify the minimum and range of damage dealt to the unit based on reqs in the standard implementation.

Describe alternatives you've considered
None yet.

Additional context
None yet.