New language feature: Contains Stmt

[marcauberer]

Compose Generator needs a feature which can search in an input data array after an element, that contains attribute <x> to have value <y>.

I had the idea to introduce a new statement type. Here is an example for the suggestion:
service.frontend contains name == "spring-maven"
or
vars contains number >= 5

As you see, this would give us the possiblity to not only check if attribute <x> is equal to value <y>, furthermore we can also check if an array contains any element with attribute <x>, having a value not equal to <y>. Or we could use more comparison operators like >, <, >=, <=.

[Splines]

Nice suggestion 👌 I originally thought of

service.frontend contains name: "spring-maven"

which is closer to the JSON syntax, but you're right: your suggestion allows for more comparisons. So yeah, let's implement it ;)