Add support for static value inputs (set by frontend) with Execution Number node

[joeyballentine]

Adds support for non-deterministic nodes... kinda.

The only node I've implemented with this is an execution number node. It's just a number that increments every time you press run. If this gets approved/merged, I plan on doing one for the current datetime as well.

This is really, really jank - but basically, I hardcode a node on the frontend that only exists on the frontend. Then, in the code that converts the flow to the backend format, I get rid of that node and replace its connections with a static value, as if that value was typed into the input.

I'm sure this is still technically "wrong" and blah blah determinism, but I think this is a good compromise as it doesn't affect how we handle caching. It's just the same as if the user were to manually change a value every time. And since this has been requested many times, I think it's worth having, even if it's a bit jank.

This only partially implements #1447. I have not added a way to manipulate this counter yet, and probably won't in this PR.

This also does not display any Navi/type info about what the value will be before running. I'm not sure how we could implement that.

[joeyballentine]

For documentation purposes: This now utilizes a new type of input for adapting static values from the frontend.

[RunDevelopment]

Other things I noticed:

1. Should the execution number reset? E.g. when the chain is reset (Ctrl+N) or a different chain is loaded? I'm not sure.
2. The current design is confusing. The output value is styled in the same way we usually style labels. E.g. this looks like an input called "19" that expects an integer.
   
   I think something similar to how Pass Through does type tags would look better.
   
   E.g. we could do:

    # Execution Number
    Current       [19]
   

   And use a big tag for the number, like model tags do.

[joeyballentine]

Should the execution number reset? E.g. when the chain is reset (Ctrl+N) or a different chain is loaded?

I don't personally think so. I plan on doing a follow-up to this where I add the ability to manually reset the number. I just haven't decided how I want to expose that yet