Allow to generate a test with #[ignore] attribute

[svenfoo]

Sometimes a test with a test resource is long-running and the documentation suggests to use the #[ignore] flag to exclude it from normal test runs. It doesn't seem possible to do that with the test_resources macro.

Maybe the macro could be extended to optionally accept a second parameter?

#[test_resources("res/input", ignore)

[almann]

FWIW, I've run into cases where this would be useful. In amazon-ion/ion-rust#217 I manually branch around the ignore case, but the test itself is not ignored.