fn validate_metric_sink_prefix(prefix: &str) -> Result<(), PlanError>Expand description
Rejects a prefix that could not start a Prometheus metric name, or that escapes the reserved
mz_metric_sink_ lane (see METRIC_SINK_PREFIX_MARKER).
The sink prepends this to every name it publishes, so prefix + name must stay a legal
family name ([a-zA-Z_:][a-zA-Z0-9_:]*, the same grammar the runtime checks each row’s
metric_name against). The prefix must therefore be at least one character long.