Add constraints to groups and test_item.

[yoavrotems]

Add the constraints functionality as we have in bench-common, to a single test in "test_item" and the entire group as well.

[avats-dev]

@yoavrotems can you guide me how to implement this? I want to contribute. Thanks.

[yoavrotems]

@avats-dev I can even do better and show you how we do it in different repos Group constraints in bench-common Original PR which has constraints per test

And in a more general way, the constraints is meant to select the correct test between multiple option, for example in Linux-bench we use it to run the same test on multiple distributions

[avats-dev]

Thanks @yoavrotems , examples are always better :smile: . I'll get started on this and get back to you if I need any help.