Conditional argument values

[kibanamachine]

Original comment by @rashidkpc:

There are lots of situations in which you want to apply a given argument value based on something. Take for example:

image asset={
 if {math 'random()' | gt 0.5} 
  then={asset 1} 
  else={asset 2}
}

What we'd need here is sort of a meta arg type called ifCondition that applies to all possible arg types and wraps them in a form for specifying the condition, and possible outcomes. We could probably expand this to switch/case later, but simply if would be a great start.