Macro observability_metric 

macro_rules! observability_metric {
    ($plugin:expr_2021, $name:expr_2021, $value:expr_2021, $($label_key:expr_2021 => $label_val:expr_2021),*) => { ... };
    ($plugin:expr_2021, $name:expr_2021, $value:expr_2021) => { ... };
}

Conditional metric recording macro