Macro mz_ore::metric

macro_rules! metric {
    (
        name: $name:expr,
        help: $help:expr
        $(, const_labels: { $($cl_key:expr => $cl_value:expr ),* })?
        $(, var_labels: [ $($vl_name:expr),* ])?
        $(,)?
    ) => { ... };
}

Define a metric for use in materialize.