Read pipeline capacity for circuit networks

[Bananycus]

TL;DR

Add the ability to read the capacity of the pipeline that a circuit wire is connected to.

What?

Add a checkbox alongside "read fluid temperature" to circuit connections to be able to read the capacity of a pipeline and output it as a signal of choice.

Why?

This feature will allow circuits to react to pipeline capacity changing, which removes the need to manually write that number in a condition somewhere if that number is needed. For example, you can make fluid train unloaders that know exactly when they can fully unload a train to maximize pressure, even if there are many more pipes built or removed.