Constant MATERIALIZE_ENRICH_RULES_HEADER 

pub const MATERIALIZE_ENRICH_RULES_HEADER: &str = "x-materialize-enrich-rules";

Response header listing the mz_ore::metrics::Rules registered on the metrics registry, as gzipped-then-base64-encoded JSON (see encode_enrich_rules). Emitted by handle_prometheus only when the caller opts in via MATERIALIZE_ACCEPT_ENRICH_RULES_HEADER.