Ability to configure minimum number of executors, much like minimum number of nodes

[JamieBriersBullhorn]

Is your feature request related to a problem? Please describe.
We have the plugin configured to always have 1 spare as this reduces the wait time for builds that need a new node, however, Jenkins is often assigning jobs to the spare, rather than using the spare executors on the other nodes. It would be nice to be able to configure the minimum number of executors, rather than nodes. Currently, the minimum spare size setting causes a new node to spin up as soon as ANY of the executors are in use on the other nodes.

Describe the solution you'd like
A config option for the minimum number of executors, that works very similar to the current minimum spare size setting. When the number of available executors falls below this value, a new node is spun up.

Describe alternatives you've considered
Trying to configure jenkins to assign new jobs to other executors before assigning to the spare, but so far no luck.

Additional context
N/A