Macro key_value 

macro_rules! key_value {
    ($key:expr, $val:expr) => { ... };
}

Create key value pairs for use in opentelemetry. These pairs can be stored and used multiple times. Opentelemetry adds key value attributes when you bump counters and histograms. so MY_COUNTER.add(42, &[key_value!(“key”, “value”)]) and MY_COUNTER.add(42, &[key_value!(“key”, “other_value”)]) will actually bump two separete counters.